petrographic characterization and evolution of the permian coal deposits of the rajmahal basin bihar india abstract lower gondwana rocks are exposed as narrow bands and discontinuous patches along the western edges of the rajmahal hills covering a large area of the bengal basin north bengal and pumea two coalfields hura and chuperbhita have productive coal mines pillar coal samples from the working coal seams of hura and chuperbhita coalfields were collected and subjected to a detailed petrographic and geochemical study using refined procedures on a large number of samples the results of the micropetrographic study reveal that the rajmahal coals are rich in liptinite and inertinite contents the fluorescence microscopy indicates that a major part identified as argillaceous mineral matter under white incident light is composed of liptinite macerals such as bituminite fluorinite and exsudatinite the volatile matter and reflectance suggest these coals are subbituminous to high volatile bituminous b c in rank the quantitative relationships among maceral and microlithotype suggest that these coals were deposited in limnic to limno telmatic conditions under very wet conditions that resulted from undisturbed peat that developed in situ along with subaquatic limnic sedimentation in swampy lakes further the gi and tpi values indicate that the hura coals were formed under oxic moor conditions with sudden episodes of flooding while the chuperbhita coals have originated in wet moors with intermittent moderate to high flooding in addition g i values suggest the formation of these coals in an upper delta alluvial valley with braided plains

a review of gold mineralization styles in finland a wide range of styles of gold mineralization has been recognized in finland including orogenic metamorphosed epithermal skarn or epigenetic ironstone hosted intrusion related nonskarn massive sulfide hosted paleoplacer and placer deposits gold production in the past was principally as a byproduct from the mining of paleoproterozoic base metal massive sulfide deposits this situation has changed during the last decade with the closure of some base metal mines and the commencement of production from recently discovered gold only deposits gold mineralization occurred during distinct episodes of crustal evolution in finland several late archean greenstone belts in the karelian craton in eastern and northern finland contain orogenic gold deposits dated at about 2 75 to 2 70 ga suggesting a coherent and pervasive tectonic and metallogenic event in the paleoproterozoic low grade the main accretionary stage of the svecofennian orogeny in finland culminated with metamorphism and deformation between 1 89 and 1 86 ga during that time intrusion related au cu mineralization took place in both syntectonic porphyry stocks and their wall rocks in and close to the archean proterozoic margin orogenic gold mineralization took place at or slightly after the metamorphic peak throughout the svecofennian domain possibly also overprinting massive sulfide and intrusion related occurrences it is notable that the largest orogenic deposits are located within discrete plutons rather than hosted by supracrustal sequences this may be a consequence of the rheological contrasts between plutons and the supracrustal lithologies the paleoproterozoic lapland domain in the northern part of the country records a protracted and complicated evolution involving multiple episodes of rifting magmatism sedimentation and alteration culminating at around 1 9 ga with the collision of the karelian craton the svecofennian fold belt to the south and the kola craton to the north these deformational events led to orogenic gold mineralization throughout the proterozoic greenstone belts of northern finland at about 1 89 to 1 86 ga during and soon after the peak of metamorphism and deformation skarnlike or epigenetic ironstone hosted deposits were also formed during the orogeny in the western and southwestern parts of the lapland domain probably somewhat later at around 1 86 ga the most favorable sites for mineralization are regionally extensive zones of early albitization that predate gold mineralization the deposition of molasselike sediments during the terminal stages of the svecofennian orogeny and weathering of both orogenic and syngenetic sulfide mineralization also prior to 1 8 ga produced placer accumulations now paleoplacers in the conglomerates of the uppermost formation of the central lapland greenstone belt placer deposits of controversial origin and provenance have also been worked for many years in the glaciofluvial sediments of northernmost finland the areas with greatest potential for the discovery of new orogenic gold deposits in finland are the late archean and paleoproterozoic greenstone belts in eastern finland and lapland respectively some fe cu au skarns or epigenetic ironstone hosted deposits have been mined in the past and there may be potential for the discovery of larger iron oxide copper gold systems in the western central lapland greenstone belt for intrusion related nonskarn mineralization the most promising areas are close to the raahe ladoga suture and the potential for additional metamorphosed and deformed epithermal mineralization exists in the tampere schist belt the significant number of gold occurrences already known in these areas highlights the potential for new discoveries

palynofloral palynofacies and carbon isotope of permian coal deposits from the godavari valley coalfield south india insights into the age palaeovegetation and palaeoclimate abstract palynological studies of the present permian sediments play a vital role in biostratigraphic and palaeoecological interpretations additionally the palynofacies analysis total organic carbon toc content and 13c value in the present study focus largely for the palaeoenvironmental and palaeoclimatic reconstruction and also provides information about processes responsible for sedimentary deposits along with their lithological counter parts the palynological investigation of 306 m deep borehole msm 25 from the somavaram area of the godavari valley coalfield has led to infer five distinct palynofloral assemblages the artinskian palynofloral assemblage i and ii guadalupian palynofloral assemblage iii and iv and lopingian palynofloral assemblage v ages have been assigned to the palynofloral assemblages based on the palynofloral evidence the distinct stable carbon isotope ratios also comprehend these ages with extreme climatic events the artinskian age 22 4 is characterized by relatively higher average 13c values whereas lowest average 13c values are observed at the lopingian age 24 0 with intermediate average 13c value 23 2 during guadalupian age in the present study the permian triassic p t transition is marked by the distinct negative carbon isotope excursion followed by a distinct recovery during the early triassic time period the relative variability of palynofacies components such as palynomorphs structured terrestrial phytoclasts opaque phytoclasts degraded organic matter om and amorphous om is related to hydrodynamic perturbations during the deposition time based on the dominance and sub dominance of the palynofacies three distinct depositional phases have been identified representing differential environmental settings the palynomorphs and structured terrestrial phytoclasts dominate the palynofacies assemblage a suggesting forest swamp environment while in the palynofacies assemblage b the dominance of degraded om and amorphous om characterize reed marshes lakeshore setting and the abundance of opaque phytoclasts in the palynofacies assemblage c indicate oxidized swamp environment

orogenic gold in the new lycksele storuman ore province northern sweden the palaeoproterozoic faboliden deposit abstract southwest of the well known skellefte district northern sweden a new gold ore province the so called gold line is presently being explored during the past decade a number of gold occurrences have been discovered in this area the largest known gold occurrence is the faboliden deposit late to post orogenic ca 1 81 to 1 77 ga revsund granite constitutes the main rock type in the faboliden area and surrounds a narrow belt of mineralized metagreywackes and metavolcanic rocks the supracrustal rocks are strongly deformed within a roughly n s trending subvertical shear zone the mineralization constitutes a 30 to 50 m wide n s striking steeply dipping zone the mineralization is commonly hosted by arsenopyrite bearing quartz veins within the supracrustal rocks the quartz veins parallel the main foliation in the shear zone gold is closely associated with arsenopyrite lollingite and stibnite and found in fractures and as intergrowths in the arsenopyrite lollingite gold is also seen as free grains in the silicate matrix of the host rock the proximal alteration zone displays positive correlation with ca s as ag sb sn w pb bi cd se and hg whereas k and na show a slightly negative correlation the hydrothermal mineral assemblage in the proximal alteration zone is diopside calcic amphibole biotite and minor andalusite and tourmaline this type of assemblage is commonly recognized in hypozonal orogenic gold deposits worldwide garnet biotite geothermometry indicates amphibolite facies in the faboliden area the ductile fabric that hosts the mineralization is also found in the margin of the surrounding revsund granitoid it is therefore suggested that at least the final stages of the gold mineralization are syn to late kinematic and the minimum age for the mineralization is thus constrained at ca 1 80 ga revsund age

8 precambrian geodynamics and ore formation the fennoscandian shield abstract compared with present day global plate tectonics archaean and palaeoproterozoic plate tectonics may have involved faster moving hotter plates that accumulated less sediment and contained a thinner section of lithospheric mantle this scenario also fits with the complex geodynamic evolution of the fennoscandian shield from 2 06 to 1 78 ga when rapid accretion of island arcs and several microcontinent continent collisions in a complex array of orogens was manifested in short lived but intense orogenies involving voluminous magmatism with a few exceptions all major ore deposits formed in specific tectonic settings between 2 06 and 1 78 ga and thus a strong geodynamic control on ore deposit formation is suggested all orogenic gold deposits formed syn to post peak metamorphism and their timing reflects the orogenic younging of the shield towards the sw and west most orogenic gold deposits formed during periods of crustal shortening with peaks at 2 72 to 2 67 1 90 to 1 86 and 1 85 to 1 79 ga the ca 2 5 to 2 4 ga ni cu pge deposits formed both as part of layered igneous complexes and associated with mafic volcanism in basins formed during rifting of the archaean craton at ca 2 5 to 2 4 ga svecokarelian ca 1 89 to 1 88 ga ni cu deposits are related to mafic ultramafic rocks intruded along linear belts at the accretionary margins of microcratons all major vms deposits in the fennoscandian shield formed between 1 97 and 1 88 ga in extensional settings prior to basin inversion and accretion the oldest cyprus type deposits were obducted onto the archaean continent during the onset of convergence the pyhasalmi vms deposits formed at 1 93 to 1 91 ga in primitive bimodal arc complexes during extension of the arc in contrast the skellefte vms deposits are 20 to 30 million years younger and formed in a strongly extensional intra arc region that developed on continental or mature arc crust deposits in the bergslagen uusimaa belt are similar in age to the skellefte deposits and formed in a microcraton that collided with the karelian craton at ca 1 88 to 1 87 ga the bergslagen uusimaa belt is interpreted as an intra continental or continental margin back arc extensional region developed on older continental crust iron oxide copper gold iocg deposits are diverse in style at least the oldest mineralizing stages at ca 1 88 ga are coeval with calc alkaline to monzonitic magmatism and coeval and possibly cogenetic subaerial volcanism more akin to continental arcs or to magmatic arcs inboard of the active subduction zone younger mineralization of similar style took place when s type magmatism occurred at ca 1 80 to 1 77 ga during cratonization distal to the active n s trending subduction zone in the west possibly interaction of magmatic fluids with evaporitic sequences in older rift sequences was important for ore formation finally the large volumes of anorthositic magmas that characterize the sveconorwegian orogeny formed a major concentration of ti in the sw part of the sveconorwegian orogenic belt under granulite facies conditions about 40 million years after the last regional deformation of the sveconorwegian orogeny between ca 930 and 920 ma

field scale estimation of the volume percentage of rock fragments in stony soils by electrical resistivity abstract analysing the properties and functional characteristics of heterogeneous soils containing several phases requires a correct estimation of the volume proportion of each phase in the case of stony soils the volume percentage of the content of rock fragments remains difficult to estimate in situ this paper presents a method that uses field spatial electrical resistivity measurements to determine the volume proportion of rock fragments based on the hypothesis that the electrical resistivity signal noise increases as the proportion of rock fragments increases a model was developed that uses the standard deviation of the apparent electrical resistivity measurements over a small area as an indicator of rock fragment contents the model was tested on three study areas of several hectares containing soil units with varying quantities of rock fragments the estimation of the rock fragment content was accurate and the error estimation of about 6 was the same order of magnitude as the bussian model 1983 the developed model strongly depends on the water content in the soil and the rock type and must be calibrated in each context nevertheless estimations of the rock fragment content in stony soils can be performed efficiently in the surface horizon as well as all along the soil profile

relationship of the presence of a non calcareous clay loam horizon to dem attributes in a gently sloping area abstract the initial objective of this study was to identify relationships between terrain attributes and soil cover over a loessic flat area covering a limestone plateau the second objective was to determine those energy factors flow path solar radiation wind intensity which could improve the understanding of morphology and soil genesis we describe 341 field observations taken over 1600 ha of an experimental area used for monitoring the water and nitrate supply in the petite beauce region 100 km to the southwest of paris for each observation several soil variables were encoded one was the presence of a non calcareous clay loam nccl horizon relief is very smooth in this region mean slope around 0 5 the main terrain attributes were derived from a digital elevation model dem at 20 20 m and assigned to the pedological observations a multiple logistic regression was used to analyse the relationship between the nccl horizon and terrain attributes special statistics were used for aspect because of the circular nature of this variable the results show a strong relationship between the presence of nccl horizon and slope gradient and slope aspect while hydrological parameters are not correlated with this horizon the mean angle of the aspect frequency of the nccl horizon was calculated and compared to the mean angles of wind direction and solar radiation balance there is a small difference between wind direction and aspect frequency of the nccl horizon this result confirms the role of wind in the spatial pattern of soils further data are required to better understand the combination of several factors role of vegetation and the age of the reshaping

paleoproterozoic high sulfidation mineralization in the tapajos gold province amazonian craton brazil geology mineralogy alunite argon age and stable isotope constraints the brazilian tapajos gold province contains the first evidence of high sulfidation gold mineralization in the amazonian craton the mineralization appears to be in large nested calderas the tapajos parima or ventuari tapajos geological province consists of a metamorphic igneous and sedimentary sequence formed during a 2 10 to 1 87 ga ocean continent orogeny the high sulfidation mineralization with magmatic hydrothermal alunite is related to hydrothermal breccias hosted in a rhyolitic volcanic ring complex that contains granitic stocks ranging in age from 1 89 to 1 87 ga cone shaped hydrothermal breccias which flare upward contain vuggy silica and have an overlying brecciated cap of massive silica the deposits are located in the uppermost part of a ring structure volcanic cone drill cores of one of the hydrothermal breccias contain alunite natroalunite pyrophyllite andalusite quartz rutile diaspore woodhouseite svanbergite kaolinite and pyrite along with inclusions of enargite luzonite chalcopyrite bornite and covellite the siliceous core of this alteration center is surrounded by advanced argillic and argillic alteration zones that grade outward into large areas of propylitically altered rocks with sericitic alteration assemblages at depth several occurrences and generations of alunite are observed alunite is disseminated in the advanced argillic haloes that envelop massive and vuggy silica or that underlie the brecciated silica cap coarse grained alunite also occurs in branching veins and locally is partly replaced by a later generation of fine grained alunite silicified hydrothermal breccias associated with the alunite contain an estimated reserve of 30 tonnes of gold in rock that grades up to 4 5 g t 1 au seven alunite samples gave 40ar 39ar ages of 1 869 to 1 846 ga with various degrees of apparent minor ar loss stable isotopic data require a magmatic hydrothermal origin for the alunite typical for high sulfidation mineralization the 34s values of most samples of alunite range from 14 0 to 36 9 sulfur isotopic alunite pyrite and oxygen isotopic alunite so4 oh temperatures range from 130 to 420 c the dh2o and 18oh2o values for alunite forming hydrothermal fluids suggest a predominance of magmatic water with a small meteoric contribution a rare sample of supergene alunite has a 34s value of 4 1 and an 40ar 39ar age of 51 3 0 1 ma other than local foliation in the volcanic rocks and recrystallization of alunite near faults the mineralization and associated alteration appears to have been remarkably undisturbed by later metamorphism and by supergene alteration the au mineralization was preserved because of burial by sediments and tuffs in taphrogenic basins that probably developed shortly after mineralization and were probably first exhumed at about 60 ma because high sulfidation mineralization forms at relatively shallow crustal levels the discoveries in tapajos province provide new perspectives for mineral exploration for the amazonian and perhaps for other precambrian cratons

fluid inclusion characteristics of auriferous quartz veins in archean and paleoproterozoic greenstone belts of eastern and southern finland fluid inclusions in auriferous quartz veins in five deposits in the archean 2 9 2 7 ga and paleoproterozoic 2 0 1 75 ga greenstone belts of eastern and southwestern finland have been characterized on the basis of their composition reconstructed isochores and decrepitation behavior the dominant fluids associated with gold mineralization are h2o co2 ch4 halite archean and h2o co2 ch4 or h2o ch4 paleoproterozoic in composition phase ratios were generally uniform h2o co2 in the archean but were variable in the paleoproterozoic in the archean au sulfide quartz veins the mineralizing fluids contain less ch4 30 mol and have higher salinities up to 39 wt nacl equiv than the corresponding fluids in the paleoproterozoic au sulfide quartz veins up to 38 mol ch4 and below 13 wt nacl equiv additionally the estimated pressure temperature conditions for gold mineralization differ markedly between the two domains mineralization occurred in a pressure temperature range of 300 to 500 c at 2 to 3 5 kbars in the archean domain and 200 to 300 c at 1 to 2 kbars in the paleoproterozoic domain decrepigrams for the archean and paleoproterozoic auriferous quartz veins show different characteristics and permit classification of the different fluid inclusion populations on a regional scale

petrographic characteristics and palaeoenvironment of the permian coal resources of the barapukuria and dighipara basins bangladesh abstract twenty seven coal samples from the barapukuria and dighipara coal basins of bangladesh were analysed for their maceral content petrographic characteristics and vitrinite reflectance the most predominant maceral was the inertinite group mean 40 followed by vitrinite mean 31 and liptinite mean 22 with considerable amounts of mineral matter mean 7 semifusinite fusinite and inertodetrinite were the most common macerals of the inertinite group collotelinite collodetrinite and vitrodetrinite were the most frequently found macerals of the vitrinite group while sporinite and cutinite were the most common in the liptinite group clay minerals occurred in higher concentrations than other minerals the measured vitrinite reflectance values ro ranged from 0 71 to 0 80 indicating a high volatile bituminous b ranking facies modelling using maceral composition and maceral indices suggested an environment of forest swamps with alternating oxic anoxic depositional conditions microlithotype dependent depositional modelling indicated evolution in limno telmatic zones under fluvio lacustrine control accompanied by the development of upper to lower deltaic plain conditions a terrestrial origin with dry forest to piedmont plain conditions was suggested by the gelification index gi and tissue preservation index tpi the lateral variation of the measured tpi values indicated an increase in the rate of basin subsidence a cross plot of the ground water index gwi vs the vegetation index vi suggested mires under ombotrophic to mesotrophic hydrogeological conditions containing herbaceous plants

metallogeny of the marco zone corvet est disseminated gold deposit james bay quebec canada the corvet est gold deposit is hosted by archean rocks of the superior province in the james bay region northern quebec canada the marco zone is hosted by amphibolite grade strongly foliated volcanic rocks and consists of disseminated gold with an apparent thickness ranging from 1 8 to 39 5 m and gold grades up to 23 g t 1 over 1 m that is continuous along strike for 1 3 km the lithotectonic sequence comprises footwall basaltic andesite amphibolite overlain by a lenticular unit of metadacite and then by hanging wall basaltic andesite amphibolite all intruded by quartz feldspar porphyry dikes dacite basaltic andesite amphibolite and quartz feldspar porphyry show a calc alkaline to transitional affinity and plot in the plate margin arc basalt field with typical volcanic arc trace element patterns mineralization consists of pyrite arsenopyrite pyrrhotite chalcopyrite and gold disseminated in deformed dacite in andesite amphibolite and in quartz feldspar porphyry dikes dacite and andesite display weak alteration characterized by silicification native gold forms inclusions in metamorphic quartz garnet feldspar arsenopyrite and pyrite or free grains interstitial to quartz feldspar pyrite chalcopyrite and arsenopyrite free gold in late quartz veins cut the serici tized metamorphic fabric inclusion and interstitial native gold within minerals annealed during metamorphism shows that gold mineralization is pre to syn metamorphic with some gold remobilized in later veins rhenium osmium dating of arsenopyrite yields an isochron age of 2663 13 ma for mineralization and a weighted average model age of 2632 7 ma for arsenopyrite formed during peak metamorphism the 2663 ma arsenopyrite has a low initial 187 os 188 os of 0 19 0 10 suggesting a juvenile crust or a mantle os source the sulfur isotope composition of marco zone pyrite and arsenopyrite shows that sulfur could have been leached from its volcanic host rocks or from reduction of archean seawater the corvet est deposit is interpreted to be an oro genic gold deposit 2663 ma deformed and recrystallized during amphibolite grade metamorphism 2632 ma

mesoarchaean aluminous rocks at storo southern west greenland new age data and evidence of premetamorphic seafloor weathering of basalts abstract metamorphosed meso to neoarchaean supracrustal rocks in the central part of the island of storo nuuk region southern west greenland show field and geochemical evidence of premetamorphic chemical alteration this alteration changed basaltic precursors into aluminous lithologies and following amphibolite grade metamorphism and penetrative ductile deformation these garnet biotite schists now resemble adjacent metapelitic schists of sedimentary origin mass balance calculations isocon method suggests that most major elements si fe mg ca na and p were leached during alteration the calculated overall net mass changes are between 18 and 45 consistent with breakdown of olivine pyroxenes plagioclase and apatite in the basaltic precursor rocks major and trace elements such as k cs rb ba pb zn la and ce were added during this alteration process whereas high field strength elements ti al zr hf and nb remained essentially immobile and were thus residually enriched interestingly th which is generally assumed to be immobile in fluids was also added during this process these chemical changes reflect interaction between a basaltic protolith and hydrous fluids that established a new equilibrium and thus a different mineral assemblage it is proposed that the premetamorphic alteration at storo was due to low temperature interaction between seawater and oceanic crust and thus essentially represents in situ submarine seafloor weathering this interpretation is consistent with the mass balances reported from well documented examples in younger settings new u pb zircon geochronology from the arc related mafic sequences at storo shows that they comprise at least two distinct age groups an older anorthosite complex dated at 3051 3 2 6 ma and a younger supracrustal sequence with age brackets between 2840 and 2710 ma the allochthonous nature of these two mafic igneous to sedimentary stacks is consistent with accretionary processes in island arc complexes and a compressional archaean tectonic setting

metallogeny of gold in the precambrian of northern europe fennoscandian gold deposits have been successfully explored in a wide range of precambrian geological environments in sweden and finland during the last two decades under explored areas still exist at other sites in the fennoscandian shield particularly in russia and norway and there is a high potential for future new discoveries of economic gold in northern europe careful geological documentation of a number of previously productive gold deposits such as haveri and saattopora finland boliden adelfors and enasen sweden and eidsvoll and bidjovagge norway is now available in the literature kutemajarvi pahtavaaraa and suurikuusikko finland and bjorkdal akerberg harnas and pahtohavare sweden represent a new generation of gold mines and recent research on these enables an improved base for formulating regional and local metallogenetic models younging trends from northeast to southwest characterize both the crust and ore forming regional patterns in the fennoscandian shield orogenic or mesothermal gold deposits are found in a wide range of host rocks and are closely linked to either the paleoproterozoic svecokarelian or the neoproterozoic sveconorwegian orogeny unlike these shear zone related deposits significant amounts of gold were concentrated in volcanogenic massive sulfide vms deposits by magmatic hydrothermal processes in conjunction with formation of paleoproterozoic svecofennian juvenile crust hundreds of gold deposits of a variety of ages and genetic styles are therefore now known in the precambrian of northern europe of which some are economic others subeconomic and still others only of scientific interest one hundred representative deposits in sweden norway finland and russia are discussed in this review literature references are provided for each of them and detailed maps show the location of each deposit or prospect listed data on tonnage and grades for the most recent exploration targets as well as the economically and historically most significant deposits show that they were formed during the entire precambrian yield of gold in the fennoscandian shield is so far confined to proterozoic deposits but the potential to find economically viable gold deposits in the russian parts of the archean greenstone belts should not be underestimated

genesis of acid sulfate alteration and au cu ag mineralization at summitville colorado the summitville au cu ag deposit occurs within a porphyritic quartz latite primarily in a zone of vuggy silica alteration characterized by leaching of all major elements except silica and iron vuggy silica is best developed between an elevation of 3 700 and 3 500 m where it occurs in irregular pipes and lenticular pods up to 70 m wide and is enclosed by up to 30 m of intense quartz alunite alteration the vuggy silica zones diminish in size with decreasing elevation and rarely exceed a width of 2 m below an elevation of 3 400 m these deep vuggy silica zones are enclosed by quartz kaolinite alteration with little or no alunite sulfide mineralization occurs primarily within the vuggy silica the sulfide assemblage changes with decreasing elevation from covellite luzonite or native gold to chalcopyrite tennantite sulfides occur lining voids or in microveinlets and are accompanied by minor kaolinitc but not by alunite gold also occurs in a near surface barite goethite jarosite assemblage that crosscuts the vuggy silica consideration of alunite kaolinitc and pyrite stability relations and of aluminum speciation at 250 degrees c indicates that a ph of 2 or below and a log f sub o 2 of 31 or 1 at 250 degrees c were necessary to produce vuggy silica alteration the chalcopyrite tennantite mineralization occurring at depth in the vuggy silica zone is indicative of less oxidizing and less acidic conditions the covellite luzonite or gold assemblage requires conditions intermediate between those necessary for vuggy silica alteration and for deep sulfide mineralization barite gold mineralization is interpreted as a near surface assemblage produced under highly acidic oxidizing conditions these textural and geochemical relationships indicate that sulfide and gold mineralization postdate the formation of vuggy silica alteration in the deposit and are not directly related to the highly acidic solutions necessary for this early acid leaching event the change from extreme acid leaching to copper sulfide and precious metal deposition may represent a transition from a magmatic vapor dominated to a liquid dominated system leading to more reducing and less acidic conditions during sulfide deposition

organic petrology of hat creek coal deposit no 1 british columbia abstract the upper eocene hat creek coal deposits of british columbia canada are one of the thickest lignite to subbituminous coal deposits of the world and comprise 350 550 m of coal samples of sedimentary organic material were taken from a 560 m interval of interbedded shale siltstone and carbonate that was penetrated by corehole 75 106 in the centre of the coal basin and the reflectances of huminite eu ulminite from coal and kerogen from the organic material were determined and petrographical analyses were made the coal deposit contains many leaf and resinite rich horizons and the reflectance of huminite in these horizons in lower than in corresponding horizons containing less liptinite when compared with huminite in adjacent coal beds the reflectance of huminite in shale is lower that in siltstone is similar and huminite associated with carbonate rocks has slightly higher reflectance values the petrological variation in the coal is mainly within the huminite group of macerals the coal at the top of the deposits is lignite r o 0 38 and becomes subbituminous c r o 0 50 at the base the inertinite content is very low indicating a low level of peat fire or oxidation the early stages of transformation of gelinite to macrinite are described the paleoenvironment appeared to be lacustrine as determined by organic petrological analysis of coals and interbedded sediments four major zones each containing many subzones were found paleoenvironments were similar for the a and c zones and also for the b and d zones

the batalha au granite system tapajos gold province amazonian craton brazil hydrothermal alteration and regional implications abstract the tapajos gold province tgp is part of the 2 10 1 87 ga ventuari tapajos or tapajos parima tectonic province of the central amazonian craton the ventuari tapajos province resulted from an ocean continent orogeny and includes two calc alkaline magmatic arcs that are represented by the cuiu cuiu complex 2 1 1 90 ga and parauari intrusive suite 1 92 1 88 ga the parauari magmatic event was accompanied by sedimentation and intrusion of post tectonic 1 88 ga calc alkaline granites and was followed by subalkaline and alkaline a type magmatism related to the 1 87 ga uatuma event the 1880 ma batalha granite consists of metaluminous to peraluminous calc alkaline to sub alkaline hornblende biotite syeno to monzo granites and shows a late to post collisional affinity intense pervasive and fissural post magmatic hydrothermal alteration linked to gold mineralization affected the batalha granite the early alteration stage involved na metasomatism represented by crystallization of interstitial albite and replacement of plagioclase and k feldspar by albite precipitation of albite caused na impoverishment and k enrichment in the hydrothermal fluid leading to microcline and biotite crystallization and pervasive replacement of older feldspars by k feldspar pervasive and fissural propylitization overprints magmatic and early hydrothermal mineral associations and is characterized mainly by epidote clinozoisite chlorite albite carbonate and sulphide fissural to pervasive sericitization was the last hydrothermal stage and led to crystallization of sericite quartz and sulphide gold mineralization was related to the last two alteration stages most importantly sericitization the hydrothermal alterations were related to exsolved magmatic aqueous fluids 500 290 c and 2 6 1 2 kbar the batalha granite shares certain characteristics with both 1 porphyry related systems biotite halogen content large alteration haloes and base metals associated with gold and 2 intrusion related gold systems reduced environment depth of emplacement and gold mineralization associated with sericitic alteration classification of the batalha gold mineralization is thus not straightforward however calc alkaline to sub alkaline subvolcanic granites similar to batalha i e with identical hydrothermal alteration patterns are associated with paleoproterozoic quartz alunite high sulphidation volcanic hosted epithermal gold mineralization in the tgp implying coeval evolution of the hydrothermal systems thus the shallower and more oxidized batalha granite may have generated a porphyry cu au type deposit this has new implications for gold exploration in the tgp apart from the known gold deposits within shear zones there is high potential for low grade large volume gold and base metal deposits

geochemical systematics and precious metal content of the sedimentary horizons of lower gondwanas from the sattupalli coal field godavari valley india abstract major trace rare earth ree and platinum group elements pge have been analysed from the carbonaceous horizons of permian barakar formation of sattupalli coal field of godavari valley to understand the provenance and depositional environment barakar formation of coal field consists of sandstone siltstone carbonaceous shale and coal seams coal is enriched in trace elements compared with the clarke s background values ferromagnesian trace elements ni cr and co are similar in range in both coal and carbonaceous shales along with large ion lithophile elements lile rb sr cs and ba high field strength elements hfse nb ta zr and ti light ree lree la sm and ag archean upper crust auc normalized ree and multielement variation patterns of the coal show a flat ree with a slight depletion in ce and eu contents in most of the samples their multielement patterns exhibit enrichment of th and u negative ta zr hf and positive ti anomalies pronounced positive anomaly occurs at zr hf and ti that are combined with both positive and negative nb and ta anomalies in carbonaceous shales and clay sandstones have a high sio 2 50 80 wt low fe 2 o 3 al 2 o 3 and moderately high k 2 o contents auc normalized ree patterns are almost flat with slight negative to no eu anomalies followed by small negative ce anomalies ce ce 0 87 0 95 with one exception their multielement patterns exhibit positive u small negative nb ta a pronounced positive zr hf anomaly followed by negative ti and v anomalies enrichment of both zr and tio 2 in some samples reflects on the mafic and felsic sources at the source region the fractionated ree patterns hree enrichment and negative eu anomalies are consistent with contribution of zircon through felsic source nb ta troughs endorse their inheritance from schistose rocks of eastern ghats complex the high al 2 o 3 yb and th yb ratios along with negative eu anomalies reflect on the ttg felsic rocks of provenance based on the geochemical available petrological and paleocurrent analysis indicate the source rocks of the barakar formation were granite granitic gneiss high grade metamorphic rocks from eastern ghats and basic rocks the provenance is located west and south east i e partly peninsular gneiss and partly eastern ghat complex the au pge contents of sattupalli coalfield have been deposited through ne sw trending post depositional transverse faults that have affected all the gondwana formations during the early cretaceous the mafic rocks present within the basement could have been the source of these elements

relative sea level changes recorded by paralic liptinite enriched coal facies cycles middle jurassic muslingebjerg formation hochstetter forland northeast greenland abstract the middle jurassic muslingebjerg formation of hochstetter forland northeast greenland consists of a succession of shallow marine sandstones encasing four coal seams formed in low lying coastal mires the seams are up to 3 45 m thick and contain coal facies cycles with high liptinite contents up to 70 vol the cycles generally start with huminite rich bright or banded coal and end with dull coal or clayey coal coaly claystone the dull coals are characterized by a high proportion of liptinite commonly resinite and often mineral matter liptodetrinite resinite and cutinite dominate the liptinite maceral group similarity in the relative proportions of the liptinite macerals in the bright and dull coals and the general association of bright coal and dull coal with a high resinite concentration suggest that the dull coals represent a residue after selective removal of ligno cellulosic tissues in the precursor peat of primarily the bright lithotype the clayey coal coaly claystone lithotypes have high contents of mineral matter and commonly contain alginite and pyrite occurrence of pyrite in levels with high diasterane c 27 c 29 ratios and sometimes also alginite in the clayey coal coaly claystone lithotypes indicates a marine influence during flooding of the mires this suggests a causal link between base level rise in the coastal mires and relative sea level rise accommodation space available for thick peat accumulations was governed by overall relative sea level rise and the dulling upward cycles record outpacing of peat accumulation due to accelerated rise in base level relative sea level the muslingebjerg formation consists of four depositional sequences beginning with a thick coal seam resting on a sequence boundary peat accumulation reflects onset of base level rise in the coastal area and the coals represent the lower part of the transgressive systems tract the overlying shoreface sandstones form the upper part of the transgressive systems tract and a progradational highstand systems tract alternatively the two lower seams in the succession may form a transgressive regressive couplet separated by a lagoonal sandstone split in this case a sequence boundary occurs at the top of the upper regressive seam the dulling upward cycles within the coal seams represent parasequences or possibly higher order sequences minimum age estimates suggest that they accumulated over 4000 11000 yr

granites and early proterozoic crustal evolution in sweden evidence from smnd upb and o isotope systematics abstract u pb zircon and whole rock rb sr sm nd and o isotope results are reported for granitoids from three proterozoic provinces in sweden that represent different crustal environments the radiometric ages span the period 1 89 1 65 ga and record events ranging from original igneous crystallisation to late metamorphic resetting these events occurred at different times in the crustal segments the o isotope ratios identify different crustal source materials for the granitoids the sm nd results indicate that the major crustal source components common to most of the granitoids formed shortly before 1 9 ga close in time to the formation of the earliest granitoids contributions from recycled archaean basement are minimal the geographically widespread occurrence of such crustal sources indicates that the period around 2 ga was of great importance for the growth of new continental crust in sweden

palaeoenvironmental reconstruction and evidence of marine influence in permian coal bearing sequence from lalmatia coal mine rajmahal basin jharkhand india a multi proxy approach abstract lalmatia coal bearing sequences belong to the barakar formation permian of lower gondwana the well developed coal bearing sequences approx 52 m exposed along the mine section have been studied to understand the depositional environment along with this a cuticle study was performed to understand the palaeoclimate with the help of the stomatal index the distribution of n alkanes n c15 to n c31 suggests major higher plant and algal dominant source input although variations are seen in the relative input steranes identified include c29 regular sterane and 4 methylsteranes the pr ph ratio varied from 0 43 to 4 26 warm temperate to subtropical palaeoclimate with fresh to brackish water bodies and reducing oxygen poor environment were inferred from the rb sr sr cu th u sr ba v v ni mean 13c value measured is 23 0 0 60 for coal and 22 6 for shale these values are well correlated with typical 13c values of the permian coal and shale the stomatal index of glossopteris leaves 280 million years was taken into account and it showed a value of 10 7 that assumes a higher level of atmospheric co2 during the barakar formation artinskian age the result also shows that permian taxon glossopteris can be used for co2 proxy during permian age the geochemical evidence suggests that towards the middle part middle coal seam of the studied section the depositional milieu was under a marine influenced marginal condition the geochemical studies and carbon isotopic ratios unequivocally suggest that fluctuating climatic conditions existed during the deposition of the lalmatia coal bearing sequence

early archean hot springs above epithermal veins north pole western australia new insights from fluid inclusion microanalysis the world s most ancient biogenic structures are found in the north pole dome of western australia where 3 47 gyr old algal mats and stromatolites are closely associated with bedding conformable and discordant laminar quartz chalcedony and barite barite rich quartz hydrothermal veins with similar mineralogy occur throughout the stratigraphy below the conformable biogenic structures with the exception of the large volume of barite these bedding conformable and discordant laminar quartz veins exhibit textures and associated hydrothermal alteration quartz chalcedony chlorite illite calcite adularia pyrite typical of epithermal deposits formed from near neutral ph fluids we characterize the physical and chemical conditions of the ancient water responsible for depositing both the discordant and conformable quartz chalcedony barite as it passed through the upper parts of the archean crust field relationships combined with new fluid inclusion data suggest that the best documented stromatolites in the north pole dome occur adjacent to quartz chalcedony bands formed from cool 120 c low salinity 3 wt nacl equiv waters higher temperature up to 300 c more saline up to 10 wt nacl equiv and co2 h2s rich ch4 aqueous fluids occur in deeper level veins rare inclusions that are unusually rich in co2 containing liquid and gaseous co2 and liquid h2o support the existence of multiple batches of hydrothermal fluids with variable densities and gas contents oxygen isotope data 8 7 3 7 suggest that the causative fluids comprised admixtures of deeply circulated surface water with variable input of magmatic components our findings reveal that the earliest life known on earth lived in and around a hydrothermal system with temperatures from 300 c at depth to 120 c near the paleosurface in an environment closely analogous to modern hot springs developed above epithermal veins evidence exists for the introduction of different batches of hydrothermal fluids with variable densities and gas contents during the development of veins these findings support previous studies that demonstrate that the processes that form epithermal deposits have been active throughout geologic time and the present day distribution of epithermal deposits is dominantly a result of preservation not process

source rock potential of the lowest coal seams of the marcelina formation at the paso diablo mine in the venezuelan guasare basin evidence for the correlation of amana oils with these paleocene coals abstract the aims of this work were to carry out a combined petrographic palynofacies and organic geochemical study of twelve drill core samples collected from the lowest coal seams in the paleocene marcelina formation paso diablo mine guasare basin northwestern venezuela to characterize crude oil samples from three wells in the nearby amana field and to evaluate oil source correlations of these crude oils with the paso diablo coal extracts the coals under study were classified as high volatile bituminous a or at the b a boundary and showed vitrinite contents between 50 0 and 89 4 vol liptinites ranging from 1 4 to 24 2 vol and inertinites in the 6 2 30 8 vol range results from organic geochemical investigations indicate that the guasare coals were generated in a limno telmatic to telmatic zone under fluctuating oxygen conditions a type iii kerogen with relatively high hydrogen content and a thermal maturity corresponding to the early oil window are proposed for these coals as supported by rock eval and petrographic data as well as biomarker interpretations oil generation potential from marcelina formation coals is probably due to the perhydrous nature of the vitrinite high bitumen contents and considerable liptinite concentrations mainly oil prone resinites and exsudatinites palynofacies observations denote a dominance of psilate pollen grains related to angiosperm plants and as expected type iii kerogens or humic coals in the studied seams the parent material of which contained a significant contribution of algae the non detection of 18 h oleanane does not preclude the fact that angiosperms are the dominant plants in the guasare paleomire on the other hand the characterization of the amana oils suggests that they all fall into a unique oil family the presence of 25 norhopanes in them could indicate paleobiodegradation and mixing from various hydrocarbon charges in the reservoir thus the crude oils from the amana field seem to be a mixture of one or more oil charges from the early mature marine carbonate source rocks of the la luna formation deposited under anoxic reducing conditions and a later pulse of hydrocarbon generation which originated from an unknown so far nonmarine source rock in this regard hydrocarbon liquid derived from the lowest marcelina coal seams may be tentatively identified as the latter oil charge also this work delineates some components of a currently subcommercial and hypothetical tertiary petroleum system identified and named as marcelina misoa c5 in the lake maracaibo region finally the coalbed gas contents of sampled coals were determined

petrographic characteristics of coal from the lati formation tarakan basin east kalimantan indonesia the present paper entails the petrographic characterization on limited coal samples drawn from the tarakan basin eastern kalimantan indonesia these coals contain a high concentration of huminite which in turn is dominated by telohuminite as a result of telohuminite content they have high gi and tpi values they contain low concentrations of liptinite and inertinite macerals the dominant microlithotype is vitrite based on the macerals and microlithotypes of these coals their paleodepositional environment has been reconstructed accordingly it is deciphered that these coals have originated under telmatic condition there was predominance of wood derived tissues and increased subsidence rate prevailed in the basin moreover during the time of their evolution there were alternate phases of oxic and anoxic moor conditions with intermittent moderate to high flooding in the basin

petrographic characteristics and carbon isotopic composition of permian coal implications on depositional environment of sattupalli coalfield godavari valley india abstract the present paper entails a study carried out on selected samples of coal and carbonaceous shales of permian age from the sattupalli open cast coal mine of godavari valley andhra pradesh to know their petrographic and chemical characteristics based on these characteristics the depositional environment has also been discussed the study reveals that these coals are sub bituminous in rank and are chemically characterized by low to medium moisture 4 3 to 8 6 wt and volatile matter 24 5 to 32 6 wt while the ash yield varies between 16 4 and 35 3 wt petrographically these coals are rich in inertinite liptinites occur in very small concentration collotelinite collodetrinite and vitrodetrinite are the main vitrinite macerals whereas fusinite inertodetrinite and semi fusinite constitute the major proportion of inertinites mean 13c value measured for coal is 22 58 0 20 and for carbonaceous shale it is 23 64 0 57 while in the organic matter of barakar sandstones the 13c is 25 2 2 1 dry periods are reflected by the abundance of inertinite in some samples while more anoxic conditions are indicated by high concentration of vitrinite in some samples seam ii of sattupalli coalfield initially formed in dry condition and gradually flooding took place due to rise in the water table during the formation of the upper part of the seam again a relatively dry phase prevailed moreover a positive correlation of 13corg with toc and a negative one with tic indicate that 13corg is being modified by 13cdic

early proterozoic bimodal volcanism hydrothermal activity and massive sulfide deposition in the boliden langdal area skellefte district sweden the boliden laangdal area in the eastern part of the skellefte district consists of an early proterozoic volcanic sedimentary sequence which includes massive sulfide deposits both the ores and their country rocks have been strongly folded and metamorphosed in the lower amphibolite facies and intruded by synorogenic 1 890 m y and late orogenic 1 750 m y granitoids the calc alkaline tholeiitic volcanic suite displays petrological and geochemical features similar to phanerozoic subduction related volcanic arcs its bimodal character suggests that extensional forces dominated in the arc during long periods probably producing incipient rifting in connection with this tensional stress large volumes of felsic pyroclastic and subordinate lava flows were extruded and large scale tectono volcanic depressions formed e g calderas this event with predominantly felsic volcanism culminated with the extrusion of genetically unrelated mafic and ultramafic rocks most of this activity occurred as submarine volcanism the convergence in space and time of a thick volcanic sequence with high permeability synvolcanic faulting and a high geothermal gradient produced by the magmatic activity favored the starting of a convective hydrothermal system where the fluid was modified seawater the hydrothermal activity produced extensive alteration in the volcanic rocks under low water rock mass ratio conditions changing their original chemical compositions and producing ore bearing hydrothermal solutions the geochemical data suggest that most of the cu and zn were leached from the volcanic rocks whereas the provenance of the pb is more uncertain because it is normally enriched in these rocks when the ore bearing hydrothermal solutions reached the sea floor they caused the deposition of massive sulfide deposits within local tectono volcanic depressions

petro chemical characterisation and depositional paleoenvironment of lignite deposits of nagaur western rajasthan india the objective of this study was to know about the depositional environment and petrographic characteristics of lignite deposits of the nagaur district rajasthan india and to decipher source rock potential lignite samples have been collected from all the working and exposed lignite seams from matasukh lignite mines of nagaur following the pillar sampling method the petrographic study has been done following the international committee for coal and organic petrology and iso norms the study has shown that nagaur lignites are mostly dominated by the huminite group of macerals followed by liptinite group the huminite group is mainly represented by attrinite textinite and ulminite whereas liptinite is represented mainly by primary liptinites such as resinite sporinite suberinite and cutinite an inertinite group of macerals occurs in the least concentration as compared to the huminite and liptinite group macerals and mainly represented by the semifusinite funginite and inertodetrinite in these lignites carbonate mineral matters are dominating over the pyrite and argillaceous mineral matter the maceral constituents present in the studied samples indicate a high proportion of type iii kerogen and are capable of generating gases only based on the reflectance of eu ulminite b maceral nagaur lignites may be classified as low rank b lignite b the study reveals that lignites originated in the bog forest under ombrotrophic to mesotrophic hydrological conditions gelification index and the tissue preservation index suggest an accumulation of peat in the marshy environment

evolution of the peak hill high sulfidation epithermal au cu deposit eastern australia the early palaeozoic macquarie arc southeastern australia hosts a variety of major late ordovician to earliest silurian subduction related deposits e g cadia east ridgeway cadia hill cowal and northparkes however there is uncertainty about whether coeval high sulfidation epithermal deposits which occur in intra oceanic metallogenic belts elsewhere in the west pacific e g lepanto and chinkuashih are also present in the macquarie arc this has led to suggestions that their absence may be due to the poor preservation potential of deposits that form at relatively shallow crustal levels in ancient rocks we present here an interpretation for evolution of the peak hill au cu deposit based on the distribution of alteration facies sulfur isotope data from several textural forms of pyrite and barite and an assessment of the regional volcanic and sedimentary facies architecture these data show that the peak hill deposit displays a distinct sub vertical zoning with a pyrophyllite and vuggy quartz core that today extends about 350 m east west and at least 550 m north south which grades out through paragonite muscovite kaolinite to a chlorite epidote alteration zone at the margin the alteration zoning reflects both lower temperatures and neutralisation of acid fluids with increasing distance from the core which represents the conduit along which hot acidic hydrothermal fluids were channelled several temporally overlapping events of silicification bladed quartz pyrite veining brecciation and pyrite veining occurred during the last stages of hydrothermal alteration although most appear to predate mineralisation au cu mineralisation was associated with late quartz pyrite barite veins and the highest gold grades occur mainly in microcrystalline quartz altered rocks in the paragonite muscovite alteration zone generally within 50 m outward from the boundary of the pyrophyllite and vuggy quartz core sulfur and lead isotope data and the characteristic zoning of ore minerals and alteration assemblages support a magmatic source for the hydrothermal fluids similarities in many of the isotopic signatures between peak hill and deposits such as northparkes support generation of the high sulfidation mineralisation during the late ordovician to earliest silurian possibly ca 440 ma metallogenic event the late ordovician to early silurian volcanic and sedimentary facies associations at peak hill are consistent with alteration and mineralisation occurring in rocks deposited in a submarine setting

the enasen gold deposit central sweden stable isotope analyses of quartz sulphides and magnetite were conducted to provide information on thermal history and source of hydrothermal fluids in the palaeoproterozoic enasen gold deposit reequilibration and homogenization of oxygen isotopes throughout the rock have apparently not occurred despite the upper amphibolite to granulite facies regional metamorphism that has affected the rocks however oxygen isotope geothermometry on a coexisting quartz magnetite pair gave a minimum temperature for peak metamorphism of around 650 c which agrees with fe mg geothermometry this suggests that grain scale equilibrium is achieved the variation in oxygen isotope ratios 18o 7 3 10 5 on quartz from the metamorphosed acid sulphate alteration zone is suggested to represent a cooling trend in the fossil hydrothermal system with higher 18o values in more superficial parts temperatures of alteration and silicification and isotopic composition of hydrothermal fluids could not be defined from the present data but it was recognized that the data is compatible with a epithermal genesis for the deposit it is suggested that alteration silicification and mineralization at the enasen gold deposit took place in a high sulphidation epithermal environment at temperatures of around 200 250 c and that the hydrothermal fluids consisted of meteoric and magmatic water a tentative reconstruction of the fossil hydrothermal system is presented sulphur isotope ratios of sulphides from the fold bearing quartz sillimanite gneiss gave 34s values close to zero indicating a magmatic source of the sulphur

petrographic characteristics and depositional conditions of eocene coals of platform basins meghalaya india abstract the coal deposits of meghalaya occur in the lakadong sandstone 25 250 m thick of eocene age the coal bearing formations are understood to have been deposited over platform areas in estuarine and lagoonal environments and subjected to recurrent marine transgressions and regressions during the eocene period there are three major groups of coalfields in meghalaya viz garo hills west daranggiri and siju coalfields khasi hills langrin and mawlong shella coalfields and minor coalfields laitryngew cherrapunji and bapung coalfields pillar coal samples have been collected from 10 seams at 15 locations and have been subjected to a detailed petrographic examination for their characterization an effort has been made to trace the path of their evolution based on coal petrography based models the quantitative petrographic analysis shows that these coals are vitrinite rich 45 0 92 9 mean 73 4 mmf basis with low concentration of inertinite 0 0 13 8 mean 3 0 mmf basis whereas the liptinite occurs in appreciable concentration 5 5 53 1 mean 22 5 mmf basis further these coals are rich in vitrite 51 6 100 mean 78 3 mmf basis the volatile matter from 38 5 to 70 0 d a f and vitrinite reflectance rom from 0 37 to 0 68 characterize these coals as per german din and north american classification approximately as sub bituminous c to high volatile c bituminous the occurrence of teleutospore single double and triple celled suggests that these coals have originated from a characteristic tertiary flora the maceral and microlithotype composition in the coal petrography based depositional models suggest that the coals of garo hills were formed in reed to open water swamps in telmatic to limnic conditions the coals of khasi hills were dominated by forest swamps and telmatic to limno telmatic conditions in addition the occurrence of large size resins suggests prolific growth of conifers in the swamps

the geology and genesis of the proterozoic massive sulfide deposit at garpenberg central sweden the garpenberg deposit of central sweden is a metamorphosed strata bound zn pb cu ag sulfide deposit intercalated in an early proterozoic supracrustal sequence of felsic metavolcanics and subordinate metasedimentary rocks which have been folded metamorphosed and intruded by synorogenic granitoids the magmatism is calc alkaline and most of the volcanic activity occurred as explosive submarine volcanism the garpenberg deposit is emplaced at the contact between metasedimentary and metavolcanic rocks and consists of 32 lens shaped orebodies stratiform zn pb cu mineralization is underlain by cu bearing stockwork ore with an extensive alteration zone of quartz phlogopite rocks with minor chlorite cordierite garnet staurolite and andalusite chemically the altered zone is enriched in magnesium iron ore metals manganese and volatiles and is depleted in sodium and calcium the proposed volcanogenic origin related to calc alkaline magmatism is supported by the morphology wall rock alteration and ore mineralogy the similarity of the garpenberg deposit to the archean massive sulfide deposits of canada and the kuroko deposits of japan supports this theory but also reveals possible differences between the compositions of precambrian and phanerozoic seawater dissimilarities in the metal ratios cu pb zn of the different deposits and their associated lithologies suggest differences in their tectonic setting the garpenberg deposit is thought to have formed in an active continental margin setting rather than in an island arc

genesis of an early proterozoic zinc deposit in high grade metamorphic terrane saxberget central sweden the saxberget strata bound zn pb cu sulfide deposit of early proterozoic age ca 1 9 ga is located in central sweden it is hosted by a supracrustal sequence of quartz feldspar and quartz mica gneisses with minor intercalations of amphibolite marble and calc silicate gneiss skarn the area has undergone several metamorphic events subsequent to syndepositional hydrothermal alteration regional high temperature and moderate to low pressure metamorphism in the upper amphibolite facies up to granite melting medium grade low pressure metamorphism associated with granite intrusions and retrograde metamorphism in the greenshist facies probably related to a burial metamorphic event the metamorphism was essentially isochemical and bulk chemical changes to the host rocks were premetamorphic and probably prelithification geochemical and petrographic evidence indicates a volcanic protholith for the gneisses and amphibolite they are the metamorphic equivalents of mainly felsic pyroclastic rocks whereas amphibolites are metamorphosed mafic volcanic rocks of basaltic composition the quartz mica gneisses represent the metamorphic equivalents of hydrothermally altered felsic volcanic rocks the intercalation of metavolcanoclastic and metasedimentary rocks marble skarn and reworked volcanics indicates a shallow water submarine environment for this ore bearing sequence geochemically the present composition of the metavolcanic rocks displays calc alkaline affinity and their bimodal character suggests a tensional environment of deposition the zn pb cu sulfide mineralization at saxberget is mainly bounded to a calc silicate horizon which laterally grades into dolomitic marble the orebodies trend in a general east west direction and dip 35 degrees to 45 degrees s with a horizontal extension on the surface of about 500 m and more than 1 500 m in the pitch direction southeast the thickness can reach up to 40 m from the footwall to the hanging wall side the ores include stratiform massive ball ore semi massive to disseminated strata bound zn pb ores in calc silicate gneiss skarn ore and disseminated cu rich ore in quartz mica gneiss large scale zoning is observed in the mineralization the massive zn pb rich ball ore dominates in the western part of the mine and disseminated skarn ore and cu rich ore are more common in the eastern part of the mine the present footwall rocks are banded felsic metavolcanics which are normally less altered and deformed than the hanging wall rocks the contact between the footwall rocks and the ores is partly defined by the ball ore which appears to represent a tectonically deformed sulfide body along a significant thrust upward the ball ore grades into or is in contact with the skarn ore which shows intense small scale folding the hanging wall of the ore bearing horizon consists of strongly altered metavolcanic and metasedimentary rocks geochemically the hanging wall rocks are depleted in na and ca and are enriched in mg and fe displaying a geochemical zoning relative to the orebodies this geochemical zoning is mineralogically expressed in the hanging wall rocks by orthoamphibole bearing and spinel bearing assemblages close to the ore and followed outward by the garnet bearing quartz mica gneisses which in turn are succeeded by the cordierite bearing quartz mica gneisses the geochemistry and interrelationships of the various petrologies strongly suggest that the stratigraphic sequence at saxberget is inverted and that the ore represents a proximal exhalite located on a subsurface alteration pipe the deposit is classified with the broken hill type of middle proterozoic stratiform sulfides which is represented in the phanerozoic by the familiar sedimentary exhalative group of stratiform zinc lead copper deposits in sedimentary rocks

geology of gulf coast lignites edited by r b finkelman and d j casagrande environmental and coal associates houston 1986 224 pp 39 00

petrographic characteristics and depositional conditions of permian coals of pench kanhan and tawa valley coalfields of satpura basin madhya pradesh india abstract this paper attempts to characterize the coals of satpura gondwana basin using a large number of pillar coal samples drawn from the working coal mines of pench kanhan and tawa pathakhera valley coalfields of this basin this westernmost gondwana basin of peninsular india is graben half graben type and occupies an area of 12 000 km2 with sedimentary fills 5000 m ranging in age from permian to cretaceous the barakar formation permian is exclusively coal bearing with a total coal reserve of nearly 2000 mt the results show that the coals of this basin are equally rich in inertinite 22 8 58 7 24 5 62 0 mmf basis and vitrinite 24 4 52 4 24 4 56 0 mmf basis the concentration of liptinite ranges from 8 8 to 23 2 9 0 26 0 mmf basis the dominant microlithotypes of these coals are inertite and vitrite with comparatively low concentrations of vitrinertite and clarite the vitrinite reflectance rom values suggests that the pench valley 0 30 0 58 coals are subbituminous c to high volatile c bituminous in rank while the kanhan and tawa valley coals 0 52 0 92 are subbituminous a to high volatile a bituminous in rank the localized enhancement of rank in the latter two basins has been attributed to the extraneous heat flow from deep seated igneous intrusions in the basin the microlithotype composition of these coals is suggestive of their evolution in limno telmatic zones under fluvio lacustrine control with the development of upper deltaic and lower deltaic conditions near the fresh water lacustrines the floral input is characteristic of forest swamps with intermittent floods leading to the development of reed moor and open moor facies particularly in the pench valley basin the gelification index gi and tissue preservation index tpi are suggestive of terrestrial origin with high tree density further moderately high gi and exceedingly high telovitrinite based tpi along with high ash content particularly for the coals of kanhan and tawa valley coalfields are indicative of the recurrence of drier conditions in the forested swamps furthermore lateral variation in tpi values is indicative of increase in the rate of subsidence vis a vis depth of the basin from east to west pench to tawa valley coalfield the ground water index gwi suggests that these coals have evolved in mires under ombotrophic to mesotrophic hydrological conditions the vegetation index vi values are indicative of the dominance of herbaceous plants in the formation of pench valley coals and comparatively better forest input in the formation of kanhan and tawa valley coals

geothermal mineralization i the mechanism of formation of the beowawe nevada siliceous sinter deposit the siliceous sinter deposit at beowawe nev has a volume of 7 71 x 10 sup 7 m sup 3 and contains 1 28 x 10 sup 11 kg silica this silica precipitated from geothermal solutions that welled up along the malpais fault a graben bounding fault sinter formation involved three steps 1 geothermal solutions saturated with quartz in the reservoir moved to the surface where they cooled and became supersaturated with amorphous silica 2 amorphous silica particles nucleated heterogeneously to produce a colloidal suspension 3 the amorphous silica particles agglomerated and were cemented together by amorphous silica precipitating in the embayments between the particles at least 5 58 x 10 sup 14 kg of geothermal solution must have been produced over time to account for the mass of silica in the beowawe deposit this fluid would have carried at least 4 95 x 10 sup 17 kj of heat to the surface 21 references 6 figures 1 table

control of coal facies to adsorption desorption divergence of coals a case from the xiqu drainage area gujiao cbm block north china abstract adsorption and desorption of coal to methane are substantially related to coal facies referring to the production potential of a coalbed methane cbm well based on analyses of the stratified channel samples from coal seams no 2 no 4 and no 9 in the xiqu drainage area gujiao cbm block north china the relationship between coal facies and adsorption desorption behaviors was first proposed and discussed using the coal facies diagrams suggested by previous investigators four types of coal facies were distinguished in the coal seams including the upper delta plain wet forest swamp i the lower delta plain fen ii the lower delta plain marsh iii and the back barrier low moor iv the upper delta plain wet forest swamp occurred dominantly developing at the bottom and top of all the coal seams both the ash yield and groundwater index gwi tend to increase from coal facies i to iv whereas the volatile compounds fixed carbon organic sulfur total sulfur micropore volume and specific surface area tissue preservation index tpi and vegetation index vi decreased which indicates changes in the vegetation types water supplements and disturbance acid base properties and redox conditions in the paleomires paleomire evolution accompanied the rise and drop of the sea level with a transgression or regression process that could be represented by the coal facies sequence coal seams no 2 no 4 and no 9 were discriminated into two three and two evolving stages respectively and these stages were characterized by complete cycles except stage 4 i from the lower delta plain marsh mudstone partings in the coal seams deposited during the highest sea level collectively paleomire environments especially the variation of vegetation types and mire water condition result in adsorption and desorption divergences among different coal facies arborescent plants decrease from coal facies i to iv as the hydrodynamic intensity increases leading to corresponding changes in botanical tissue preservation medium oxidizability mineral content and ultimately adsorption and desorption behaviors in view of the gas content and desorption capacity of the coal layers in the same coal seam the layers from the upper delta plain wet forest swamp may have the best potential for cbm drainage followed by those from the lower delta plain fen and marsh while those from the back barrier low moor may have the worst potential

early svecofennian stratigraphy of southern and central norrland sweden and the possible existence of an archaean basement west of the svecokarelides abstract the stratigraphy of supracrustal sequences of seven different areas in southern and central norrland sweden are compared all the sequences belong to the svecofennian part of the early proterozoic svecokarelian fold belt it is concluded that quartzites and meta arkoses are usually found at high stratigraphic levels they are sparse or absent in the north but are more abundant in southern norrland this may suggest that a granitic archaean or early proterozoic basement was exposed to erosion somewhere southwest of the regions under consideration future research should aim at clarifying the age and extent of this basement and the provenance of the various metasedimentary rocks

observations on indian permian gondwana coals under fluorescence microscopy an overview abstract macerals like sporinite cutinite suberinite and resinite of the liptinite group have been insufficiently recorded in indian permian gondwana coals until the fluorescence microscopy came into existence with the introduction of this technique macerals like bituminite fluorinite and exsudatinite were convincingly recognized and alginite and liptodetrinite normally mistaken for mineral matter under normal reflected light in routine coal petrographic analysis were identified with certainty thus fluorescence microscopy has added certain new macerals to the tally of the liptinite group and has increased their overall proportion in indian gondwana coals in addition to the liptinite group collodetrinite desmocollinite and a certain fraction of collotelinite telocollinite macerals of the vitrinite group were found to be fluorescing with dull reddish brown to dark brown colours certain semifusinite and inertodetrinite macerals of inertinite group were also found to fluoresce with almost identical intensity and colour as that of the associated perhydrous fluorescing vitrinite contributions of degraded resinite algal matter and bitumen in the formation of perhydrous vitrinite have been established the fluorescence behaviour of inertinite appears to be related with its genesis from partial oxidation of resin bitumen impregnated cell walls

fuchsite aluminium silicate rocks in archaean greenstone belts are they metamorphosed alunite deposits for the origin of fuchsite and alusite corundum rocks occurring as lenses within ultramafic schists at o briens zimbabwe a model is presented according to which an ultramafic komatiite flow is altered locally during postvolcanic near surface processes anto chromiferous alunite that in turn broke down during subsequent low grade metamorphism into fuchsite or andalusite or ruby or assemblages thereof depending on the availability of silica and on solution chemistry pseudomorphs of corundum and andalusite after preexisting euhedral alunite or after other minerals with alunite structure support this model fuchsite kyanite and alusite quartz schists from the yilgarn block of western australia forming conformable layers in metasediments may also have originated from alunitequartz rocks but no textural evidence could be provided however in neighboring kyanite and alusite quartzites the typical cross sections of leached out alunite group minerals as well as the mineral natrojarosite were discovered within the metamorphic quartz fabric which appears to indicate that alunite type minerals coexisted during metamorphism with quartz and kyanite alunite bearing sedimentary educts are not necessarily of postvolcanic origin but may also form under specila climatic conditions

a comparison of alteration assemblages associated with archean gold deposits in western australia and paleozoic gold deposits in the southeast united states a comparison of high alumina mineral assemblages spatially associated with the haile and brewer gold deposits in the paleozoic carolina slate belt csb of the southeast united states and the sons

an oxygen isotope and geochemical study of meteoric hydrothermal systems at pilot mountain and selected other localities carolina slate belt several epigenetic mineral deposits in the ca1rolina slate belt are intimately related to meteoric hydrothermal systems of late precambrian and early paleozoic age at pilot mountain low 18 o rocks correlate well with zones of strong silicic alteration and alkali leaching accompanied by high alumina minerals sericite pyrophyllite andalusite or topaz and anomalous concentrations of cu mo sn b and au the alteration occurs within andesitic volcanic and volcaniclastic rocks and is associated with a subvolcanic dacite porphyry stock on the southeastern slope of the mountain tilting and erosion have exposed an oblique section through the original system interpreted to expose shallower rocks to the northwest a 4 km 2 central zone of slight 18 o depletion delta 18 o sub whole rock 4 3 6 1ppm occurs on the broad and resistant silicifled western flank of pilot mountain predominantly within quartz sericite schist and quartz granofels containing pods of high a1 minerals a magmatic source for much of the sulfur and metal is likely and a subordinate magmatic water component in the fluid of the central zone is possible this central zone is surrounded by a 30 km 2 peripheral zone of low 18 o sericite schists chlorite sericite schists and andesitic volcanic rocks delta 18 o sub whole rock 3 8ppm with the lowest values 1 4ppm occurring in intensely sericitized rocks on the eastern flank of pilot mountain near the apex of the dacite porphyry stock rhyolites of the uwharrie formation delta 18 o 3 8 6 3ppm are not as strongly altered as nearby andesites and may postdate the hydrothermal alteration the fluid calculated to be in equilibrium with the lowest 18 o quartz veins and country rocks at 300 degrees or 50 degrees c would have delta 18 o approximately 4 5 or 2 0 per mil whereas analyses of radiating pyrophyllite indicate equilibrium with a fluid having delta d approximately 30 per mil consistent with a slightly 18 o shifted low latitude meteoric water subsequent greenschist metamorphism caused intermineral isotopic reequilibration in several samples and may have modified preexisting alteration assemblages but it did not destroy the large delta 18 o anomaly produced by meteoric hydrothermal activity at pilot mountain reconnaissance studies of other alteration zones in the carolina slate belt have so far disclosed the involvement of meteoric hydrothermal fluids at the snow camp pyrophyllite deposit at the hoover hill and sawyer au mines and probably at the haile and brewer au mines

metal sources in the early proterozoic svecofennian terrain of central sweden pb isotope evidence the lead isotope composition of three cu zn pb sulfide deposits and one au deposit in the early proterozoic svecofennian of central sweden reveals the existence of two distinct lead sources in the region rockliden and enstern contain lead of upper crustal affinity and are isotopically homogeneous lead in these deposits probably originates from archean derived detritus which was well homogenized by sedimentary processes and deposited over large areas as a component in early proterozoic sedimentary and tuffaceous rocks lead isotopic homogeneity within the tjarnberget and enasen deposits is less pronounced and the less radiogenic character of the lead suggests a source of mantle affinity in areas where metasedimentary rocks are absent or contain very little archean derived material the isotopic signature of mantle derived volcanic rocks is reflected in the ore lead this approach is also applicable to other svecofennian deposits together with deposits in west central finland the rockliden deposit constitutes the northern boundary for lead of upper crustal affinity i e archean derived lead in svecofennian sulfide deposits

lead isotopic evidence for the origin of 1 8 1 4 ga ores and granitoids in the southeastern part of the fennoscandian shield abstract new data for the lead isotopic composition of galena from ore deposits related to 1 8 1 4 ga granitoids in the southeastern part of the fennoscandian shield are presented and discussed together with earlier published information on granitoids and associated ore deposits two types of sulphide deposits genetically related to the granites can be recognized based on general metallogenetic features and isotopic composition granite hosted deposits including sn bearing greisen veins in rapakivi granites and peri intrusive deposits including contact metasomatic skarn deposits like pitkaranta and gruvasen in addition epigenetic deposits with a spatial but not a genetic link to the granites occur at various sites an important metallogenetic belt related to 1 7 1 5 ga granitoids can be followed in an east west direction across the shield from lake siljan in sweden to salmi at lake ladoga within this belt a major difference in metal derivation can be recognized ore deposits southwest of the raahe ladoga line i e in areas without archaean basement indicate metal derivation from remelted 1 9 ga svecofennian crust whereas ore deposits in areas underlain by archaean rock units indicate metal derivation from highly metamorphosed archaean sources

the diversification of paleozoic fire systems and fluctuations in atmospheric oxygen concentration by comparing silurian through end permian 250 million years myr charcoal abundance with contemporaneous macroecological changes in vegetation and climate we aim to demonstrate that long term variations in fire occurrence and fire system diversification are related to fluctuations in late paleozoic atmospheric oxygen concentration charcoal a proxy for fire occurs in the fossil record from the late silurian 420 myr to the present its presence at any interval in the fossil record is already taken to constrain atmospheric oxygen within the range of 13 to 35 the fire window herein we observe that as predicted atmospheric oxygen levels rise from 13 in the late devonian to 30 in the late permian so too fires progressively occur in an increasing diversity of ecosystems sequentially data of note include the occurrence of charcoal in the late silurian early devonian indicating the burning of a diminutive dominantly rhyniophytoid vegetation an apparent paucity of charcoal in the middle to late devonian that coincides with a predicted atmospheric oxygen low and the subsequent diversification of fire systems throughout the remainder of the late paleozoic first fires become widespread during the early mississippian they then become commonplace in mire systems in the middle mississippian in the pennsylvanian they are first recorded in upland settings and finally based on coal petrology become extremely important in many permian mire settings these trends conform well to changes in atmospheric oxygen concentration as predicted by modeling and indicate oxygen levels are a significant control on long term fire occurrence

epithermal sinters of paleozoic age in north queensland australia silica sinters deposited from hot springs have been found associated with volcanic rocks of late devonian to late carboniferous age in north queensland australia these deposits have many features in common with modern hot spring sinters such as those of the taupo volcanic zone in new zealand they occur associated with subaerial volcanic rocks and are locally found with air fall tuffs and fluvial and lake deposits in which hydrothermal eruption breccias are common the associated rocks are extensively hydrothermally altered and are cut by silica veins showing characteristic epithermal vein textures the silica veins contain low salinity fluid inclusions trapped at epithermal temperatures and there is evidence of boiling textures preserved in the sinters are identical to those found in modern sinters they include columnar structures similar to bacterial stromatolites described from yellowstone national park as well as striated surfaces apparently resulting from silica deposition on filamentous algae plant fossils including oxroadia gracilis are abundant criteria applied to identify these ancient sinters may be applied to other possible sinter deposits and may provide evidence indicating the level of exposure of the former geothermal system which may be an important guide in exploration for epithermal precious metal deposits

the depositional evolution of the svecofennian supracrustal sequence in finland and sweden abstract on the basis of six new zircon ages from metavolcanic rocks together with other isotopic geophysical and geological data the chronological and tectono stratigraphic evolution of the early proterozoic svecofennian supracrustal rocks in finland and sweden are discussed these data suggest that a nw se displacement from the bothnian bay to lake ladoga and a sinking of the southwestern block was initiated 1950 2000 ma ago accumulation of pelitic sediments and greywackes on the subsiding archaean basement continued until about 1860 ma in south central and northern sweden shallow submarine and subaerial volcanics were extruded 1880 1890 ma ago the thick sedimentary piles and volcanic rocks were subsequently intruded by plutonic rocks forming large batholiths 1860 1890 ma ago

revisiting the paleomires of western india an insight into the early paleogene lignite corridor abstract the paleocene eocene lignite sequences of western india occur in the bikaner nagaur barsingsar gurha and kasnau matasukh lignite seams and barmer kapurdi and giral lignite seams basins of rajasthan whereas those in the cambay vastan rajpardi and tadkeshwar lignite seams saurashtra bhavnagar upper and lower lignite seams and kachchh matanomadh and panandhro lignite seams basins are located in gujarat the position of the cambay basin gujarat being closer to the equator during the early eocene period makes it pertinent to understand the variations in petrographic and geochemical constituents of gujarat and rajasthan lignites in space and time floral growth which largely depends on the climate of the region and its geographical location has an important role in the formation of mire nevertheless the peat forming plant communities nutrient supply bacterial activity types of deposition temperature ph and redox potential impart various characteristics to coal and are reflected in macerals black bands in gujarat and rajasthan lignites are strongly gelified compared to brownish bands and are stratified in nature they are dominantly composed of huminite maceral group while liptinites and inertinites occur in subordinated amount these lignites of gujarat and rajasthan have high values of gelification index gi and low tissue preservation index tpi indicating thereby a continuous presence of wet condition in the basin and slow subsidence rate however due to fluctuating water level in the basins few sections experienced relatively oxic episodes indicated by relatively high inertinite content study of the ground water index gwi and vegetation index vi of these lignites indicates rheotrophic to mesotrophic hydrological condition the study revealed that the lignites of rajasthan and gujarat were formed during the transgressive phase under coastal marshy setting however there were intermittent episodes of fluvial activities which gave rise to supratidal flood plains

chemical imprint of highly metamorphosed volcanic hosted hydrothermal alterations in the la romaine supracrustal belt eastern grenville province quebec the la romaine supracrustal belt and the southeastern end of the wakeham group in the eastern grenville province canada host a series of pinwarian 1 50 ga felsic dominated volcanic centres metamorphosed at amphibolite to granulite facies during the grenville orogeny the centres are interpreted as being related to the emergence of rhyolitic domes in shallow marine intra arc basins within the active pinwarian continental magmatic arc high grade metamorphosed hydrothermal alteration zones are intimately associated with pyroclastic deposits composing these volcanic centres and an overlying composite amphibolite unit they comprise layers of rhyolitic metatuff bearing networks of aluminous nodules and veins migmatized garnet biotite sillimanite gneiss with well preserved volcanic fragments and mottled quartz cordierite gneiss with textures similar to those of vuggy silica facies alteration zones of ironstone carbonate and calc silicate rocks garnetite diopsidite epidosite and sulphide mineralizati

field based and spectral indicators for soil erosion mapping in semi arid mediterranean environments coastal cordillera of central chile the coastal cordillera of central chile is naturally sensitive to soil erosion due to moderate to steep slopes intense winter rains when the vegetation cover is scarce and deeply weathered granitic rocks in 1965 60 per cent of its surface was moderately to very severely eroded today this process is still largely active but no data are currently available to evaluate the real extent distribution and severity of soil degradation on a regional scale this information is vital to support efficient soil conservation plans a multi scale approach was implemented to produce regional land degradation maps based on remote sensing technologies fieldwork has shown that the surface colour or redness and the density of coarse fragments are pertinent erosion indicators to describe a typical sequence of soil degradation in the context of mediterranean soil developed on granitic materials and micaschists field radiometric experiments concluded that both factors influence the reflectance of natural surfaces and can be modelled using radiometric indices accessible from most satellites operating in the optical domain i e redness index and brightness index finally the radiometric indices were successfully applied to spot images to produce land degradation maps only broad classes of erosion status were discriminated and the detection of the degradation processes was only possible when most of the fertile layer had already been removed this technology provides decision making information required to develop regional soil conservation plans and to prioritize actions between catchment areas especially in vast inter tropical regions where spatialized data are not always readily available copyright 2006 john wiley sons ltd

hydrothermally enhanced magnetization at the center of the haughton impact structure haughton is a 24 myr old mid size apparent diameter 23 km complex impact structure located on devon island in nunavut canada the center of the structure shows a negative gravity anomaly of 12 mgal coupled to a localized positive magnetic field anomaly of 900 nt a field expedition in 2013 led to the acquisition of new ground magnetic field mapping and electrical resistivity datasets as well as the first subsurface drill cores down to 13 m depth at the top of the magnetic field anomaly petrography rock magnetic and petrophysical measurements were performed on the cores and revealed two different types of clast rich polymict impactites 1 a white hydrothermally altered impact breccia not previously observed at haughton and 2 a grey impact breccia with no macroscopic sign of alteration in the altered core gypsum is present in macroscopic veins and in the form of intergranular selenite associated with colored and zoned carbonate clasts this altered core has a natural remanent magnetization nrm four to five times higher than materials from the other core but the same magnetic susceptibility their magnetization is still higher than the surrounding crater fill impact melt rocks x ray fluorescence data indicate a similar proportion of iron rich phases in both cores and an enrichment in silicates within the altered core in addition alternating field demagnetization results show that one main process remagnetized the rocks these results support the hypothesis that intense and possibly localized post impact hydrothermal alteration enhanced the magnetization of the clast rich impact melt rocks by crystallization of magnetite within the center of the haughton impact structure subsequent erosion was followed by in situ concentration in the subsurface leading to large magnetic gradient on surface

geology geochemistry and origin of high sulfidation cu au mineralization in the nansatsu district japan the nansatsu district of southern kyushu has been the site of calc alkaline volcanism for the last 10 m y shifting eastward with time associated hydrothermal activity followed deposition of the volcanic host rocks by about 0 5 m y and was characterized by interaction of magmatic fluids with meteoric water under epithermal conditions resulting in the formation of high sulfidation cu au deposits at kasuga iwato and akeshi the orebodies consist of 95 wt percent sio 2 and result from leaching of the original andesite lava and pyroclastic flows by acid chloride sulfate waters these are inferred to have formed when magmatic vapors containing hcl and so 2 condensed into meteoric water the residual silica now quartz orebodies are best developed where the host was initially permeable the margins of the quartz bodies are abrupt with narrow 1 2 m halos representing the reaction front of acid waters isochemically dissolving the host rock the halo comprises alunite strongly zoned in na and k with p rich cores dickite and or kaolinite or pyrophyllite grading out into illite and interlayered illite smectite clays and finally propylitic alteration this pattern is characteristic of deposits of this type throughout the world for example at summitville colorado and lepanto philippines mineralization occurred after initial leaching by the vapor condensates with metals transported by a dense magmatic fluid mixing with meteoric water and the subsequent temperature decrease caused the general decrease in grade toward the margin of the quartz bodies ore grades are restricted to the quartz bodies gold is most closely associated with enargite and pyrite later minerals include covellite and then sulfur the last stage of activity was steam heated with descending waters oxidizing sulfides to goethite and locally remobilizing au into fractures this varies in degree between deposits erosion exposed the orebodies to supergene weathering continuing the sulfide oxidation and au remobilization stable isotope results indicate that hypogene alunite formed from a mixture of magmatic fluid delta 18 o 7 or 2 per thousand delta d 25 or 5 per thousand similar to nearby active volcanic discharges with local meteoric water in contrast the clays in the marginal halo have isotopic compositions indicating a delta 18 o shift of 6 to 8 per mil from local meteoric water values probably due to water rock interaction and the delta 18 o values of residual silica quartz may also be due to meteoric water domination fluid inclusion study of postmineralization quartz crystals indicates that the fluids had a salinity of about 1 wt percent nacl equiv during late quartz growth though there is evidence in one sample for higher salinity fluid having been present up to 30 wt percent nacl equiv some inclusions contain daughter minerals of halite and sulfur the t h values of over 1 000 measurements on late quartz from the ore zones indicate that the mean temperature during that stage ranged from 200 degrees c at akeshi to about 200 degrees c at iwato and 230 degrees c at kasuga the presence of vapor rich inclusions some with t hv similar to t hl indicate the presence at times of a two phase fluid in the center of the ore zones with depths of about 150 to 300 m below the paleowater table the mineralizing fluid was relatively oxidized sulfide sulfate ratio about 3 1 close to pyrite alunite coexistence under these redox conditions a ph of 3 and over a temperature range of 200 degrees to 300 degrees c aucl 2 super complexing may dominate over hau sh 2 at salinities above about 2 wt percent nacl several conditions are conducive for high sulfidation mineralization to occur 1 a crystallizing magma exsolves a fluid with lower pressure conditions favoring metal fractionation from melt to fluid 2 the exsolved fluid separates into vapor and saline liquid phases due to immiscibility with the latter being metal rich 3 the gas rich hcl and so 2 h 2 s vapor ascends to the surface with at least a portion condensed into meteoric water forming an acid fluid which leaches the host rock to create permeable zones for later mixing and 4 the dense metal bearing fluid also ascends into this leached zoned and precipitates cu sulfosalts sulfides and au upon mixing with meteoric water if the saline liquid is not released from its source adjacent to the magma due to lack of fracturing or if there is a strong hydraulic gradient caused by high relief only the vapor related stage may occur this will leave leached barren rock which is characteristic of many eroded volcanic terranes

influence of rock fragments on the water retention and water percolation in a calcareous soil abstract the water retention properties of a calcareous soil containing rock fragments have been determined in the laboratory thanks to pressure plate measurements done on both the fine earth and the rock fragments from the soil the available water content awc has been calculated from these data we have shown that when the rock fragments are neglected the awc can be overestimated by 39 when we do not neglect their volume but when their hydraulic properties are not considered the awc can be underestimated by 34 by using a reservoir model we have also calculated the effect of rock fragments on water percolation to groundwater depending of the climatic characteristics of the year the underestimation of percolation when we neglect the rock fragments can reach up to 14 9 and the overestimation when we neglect their hydraulic properties can be equal to 15 8 these findings emphasise the role of the rock fragments on the water supply in stony soils