structural and geochronologic data from the shin jinst area eastern gobi altai mongolia implications for phanerozoic intracontinental deformation in asia abstract the complex geology of central asia records significant phanerozoic growth and deformation of continental lithosphere yet many questions about the timing and mechanisms of these processes remain the gobi altai of southwestern mongolia preserves much of this history in exposed mountain ranges and sedimentary basins the shin jinst area near latitude 44 21 to 44 32 longitude 99 35 to 99 25 contains important evidence of paleozoic growth and accretion as well as subsequent mesozoic and cenozoic deformation detailed mapping and structural data including data sets on folds and cross cutting faults point to repeated episodes of deformation and add to recent work that documents triassic and jurassic compression as well as cenozoic tectonic activity in this region new 40ar 39ar data are interpreted to record permian to jurassic convergent margin processes in particular these data in combination with previous studies suggest that southern mongolia records protracted deformation throughout the jurassic that likely resulted from compression associated with the subduction zone at the southern margin of asia at that time

lithological discrimination based on statistical analysis of multi sensor drill core logging data in the matagami vms district quebec canada in mineral exploration traditional core logging is largely based on the visual inspection of drilled cores a process which is often subjective and non reproducible however a number of physical chemical and mineralogical properties of rocks can now be measured at high spatial resolution on drill cores the resulting large multiparameter databases can help geologists to quantitatively discriminate between lithologies study hydrothermal alteration and potentially vector towards mineralization multivariate statistical methods are important tools to assist geologists in interpreting such large databases we present an application of model based cluster analysis in the matagami base metal mining district more specifically to improve lithological discrimination at the zinc rich bracemac and mcleod volcanogenic massive sulfide vms deposits the model based cluster analysis method is able to efficiently discriminate different geological units encountered even in cases where two units are visually similar or in the presence of strong hydrothermal alteration

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

great jurassic thrust sheets in beishan north mountains gobi areas of china and southern mongolia abstract jurassic thrust sheets with minimum displacements of 120 180 km have been discovered within the hercynian indosinian orogenic belt of the beishan of china and south gobi area the thrusts strike e w extend over 1200 km in length and carried meso proterozoic massive dolomitic limestones over strata ranging from neoproterozoic cryogenian and terminal proterozoic to lower middle jurassic slip linear plots based on kinematic indicators such as slickenlines and groove lineations fiber lineations and drag folds adjacent to the fault surface vergence of folds and imbricated thrusts in the upper plate indicate northward movement in the beishan area to the west and southward movement in the south gobi area to the east the two major thrust faults the beishan thrust and south gobi thrust are presumably separated by a major tear fault the ruo shui fault the major thrust faults were later deformed into a series of e w antiforms and synforms and the sheets are separated due to erosion into a number of klippen mainly located on synforms of the major faults the yagan metamorphic core complex which is a result of an extensional event that postdates the thrust event yields an 40 ar 39 ar plateau age of 155 1 10 ma and rb sr isochron age of 153 6 2 ma the thrust sheets formed during the late middle jurassic long after the closure of any oceans in the study area previously reported for this region and are ascribed to a phase of intracontinental deformation the closing of the jurassic tethys or retroarc deformation behind an active continental margin at the southern edge of asia prior to the tethyan collision or and the closing of mongolo okhotsk oceans might be responsible for this event

strike slip tectonics and granite petrogenesis transpression is a process that thickens the crust and therefore in obliquely convergent orogens as in normally convergent orogens there is the potential to generate granitic melts individual transcurrent shear zones may not only control the ascent paths siting and emplacement mechanisms of plutons but they may also cause the genesis of the granitoids themselves two contrasting situations are examined in the hercynian shear zones of iberia thickening together with hydrous fluxing along shear zones created intracrustal wet melting of fertile gondwanan sediments to produce syntectonic granites in the northern part of the british caledonides the association of compositionally expanded granitoids with a major mantle component and transcurrent shear zones may be explained by melting of continental crust at the lower limits of crustal transpressional faults detaching into the moho

tracing mineralogy and alteration intensity using the spectral alteration index and depth ratios at the northwest zone of the lemarchant volcanogenic massive sulfide deposit newfoundland canada

jarosite occurrence in the deccan volcanic province of kachchh western india spectroscopic studies on a martian analog locality the sulfate mineral jarosite is considered a key indicator of hydrous acidic and oxidizing conditions on the surface of early mars here we report an analog terrestrial locality hosting jarosite from matanumadh kachchh western india using detailed spectroscopic studies on weathered basalts of the deccan volcanic province and overlying tuffaceous shales and sandstones of the matanumadh formation hyperspectral data in the visible near infrared 350 2500 nm to midinfrared 4000 400 cm 1 region of the electromagnetic spectrum and x ray diffraction patterns have been acquired on samples collected from the field to detect and characterize the hydrous sulfate and phyllosilicate phases present at the studied site hydrous sulfates occur in association with al rich phyllosilicates kaolinite that overlie a zone of fe mg smectites in altered basalts jarosite is found within both saprolitic clay horizons altered from the basalt and within variegated sandstone and shale clay units overlying the saprolite it mostly occurs as secondary veins with or without gypsum jarosite is also seen as coatings on kaolinite clasts of varying shapes and sizes within the tuffaceous variegated sandstone unit we argue that the overall geological setting of the matanumadh area with this unusual mineral assemblage developing within altered basalts and in the overlying sedimentary sequence mimics the geological environment of many of the identified jarosite localities on mars and can be considered as a martian analog from this perspective

palaeomagnetic study of vendian and early cambrian rocks of south siberia and central mongolia was the siberian platform assembled at this time abstract a palaeomagnetic study of vendian and early cambrian sediments from the angara block of the siberian platform shaman 52 08 n 108 83 e and minya 58 0 n 110 0 e formations and the tuva mongolian block tsagan olom and bayan gol formations 46 76 n 96 37 e isolated three different components of magnetization through thermal demagnetization the stable high temperature characteristic remanence directions show both normal and reverse polarities the mean palaeopoles computed after these high temperature components are 32 0 s 71 1 e dp dm 6 9 13 8 for the vendian shaman formation 10 sites 80 samples 33 7 s 37 2 e dp dm 8 6 14 7 for the vendian minya formation 12 samples 22 8 s 28 4 e dp dm 10 8 21 6 for the vendian tsagan olom formation 4 sites 25 samples and 21 4 s 167 1 e dp dm 9 6 19 1 for the early cambrian bayan gol formation 6 sites 49 samples from a compilation of vendian and early cambrian palaeopoles from the anabar angara and aldan blocks of the siberian platform and tuva mongolia block we propose a model where these blocks were situated in an equatorial to low south palaeolatitude position with their present day southern boundaries facing the north pole from the analysis of the scatter of these poles we conclude that the siberian platform might not have fully amalgamated by this time and that significant rotations occurred after the early cambrian our new palaeopoles for the tuva mongolia block together with previously published ones show that this block was already adjacent to siberia by the vendian and early cambrian we propose that the large counterclockwise rotation of the tuva mongolia block with respect to angara block could mark the end of the closure of the part of the palaeo asian ocean separating these two blocks and could account for the occurrence of vendian early cambrian ophiolites in the region

the glacier creek cu zn vms deposit southeast alaska an addition to the alexander triassic metallogenic belt the glacier creek volcanogenic massive sulfide vms deposit alaska is hosted within late triassic oceanic back arc or intraarc rift related bimodal volcanic rocks of the allochthonous alexander terrane known as the alexander triassic metallogenic belt the alexander triassic metallogenic belt is host to the world class greens creek zn pb ag vms deposit near juneau in the south and the giant windy craggy cu co vms deposit in british columbia about 250 km to the north the glacier creek deposit located 80 km southeast of windy craggy consists of four tabular massive sulfide lenses within a bimodal mafic volcaniclastic and rhyolitic sequence the mineralization hosting stratigraphy is folded by a deposit scale anticline and offset by a thrust fault near the axial surface of the fold a resource of 8 13 mt has been inferred from drilling with grades of 1 41 cu 5 25 zn 0 15 pb 0 32 g t au and 31 7 g t ag six main mineralization types are recognized dominated by massive barite sphalerite pyrite which is replaced at the base and center of the main lenses by massive and semimassive chalcopyrite pyrite quartz the flanks and tops of the lenses are carbonate rich and consist of interbedded calcite dolomite barite and sulfide resedimented massive barite sulfide and mineralized massive carbonate rocks tuffaceous hydrothermal sediment with a distinct positive eu anomaly overlies the massive sulfide pyrrhotite and chalcopyrite in stringers constitute the main feeder zone stringer style sphalerite pyrite mineralization occurs above and below the lenses fe poor sphalerite is dominant throughout the lenses whereas fe rich sphalerite occurs at the stratigraphic top and bottom of the lenses in pyrrhotite rich zones galena tennantite tetrahedrite and arsenopyrite are the most important trace minerals within massive barite sphalerite pyrite mineralization which is generally enriched in sb hg and tl mineralization related gangue minerals include barite quartz barian muscovite calcite dolomite albite chlorite hyalophane and celsian four types of alteration are recognized in the dominantly basaltic host rocks pervasive muscovite rich alteration quartz pyrite alteration associated with sulfide stringers stratabound carbonate bearing alteration and background epidote bearing alteration mass balance calculations indicate gains of s fe si and k with coincident losses of ca na and mg in all of the alteration types trace elements tl sb hg ba zn cu and as were added to the rocks whereas sr was lost short wavelength infrared swir spectroscopy shows an increase in the wavelength of the aloh absorption feature toward mineralization at a scale of 30 to 50 m coincident with a general decrease in the na k and al and increase in the fe mg and ba content of muscovite the glacier creek deposit is transitional in character between greens creek which is more zn pb and precious metal rich and the windy craggy deposit which is more cu and co rich reflecting differences in the basement rocks and depositional settings within the alexander triassic metallogenic belt mineral chemical studies and sulfur isotope data suggest that the glacier creek deposit formed under initially oxidized and sulfate rich conditions that evolved to more reduced conditions in the latest stages of mineralization the abundant argillite and presence of hyalophane rather than barite in the immediate hanging wall of the deposit may be an indication of a deepening basin and development of local anoxia similar to greens creek

gps measurements of crustal deformation in the baikal mongolia area 1994 2002 implications for current kinematics of asia 1 we present new geodetic results of crustal velocities over a large part of northern asia based on gps measurements in the baikal rift zone and mongolia spanning the 1994 2002 period we combine our results with the gps velocity field for china of wang et al 2001 and derive a consistent velocity field for most of asia we find contrasted kinematic and strain regimes in mongolia with northward velocities and n s shortening in westernmost mongolia but eastward to southeastward motion and left lateral shear for central and eastern mongolia this eastward to southeastward motion of central and eastern mongolia is accommodated by left lateral slip on the e w trending tunka bolnay and gobi altay faults 2 1 2 mm yr 1 2 6 1 0 mm yr 1 and 1 2 mm yr 1 respectively and by about 4 mm yr 1 of extension across the baikal rift zone consequently 15 of the india eurasia convergence is accommodated north of the tien shan by n s shortening combined with dextral shear in the mongolian altay and by eastward displacements along major left lateral strike slip faults in central and eastern mongolia we find a counterclockwise rotation of north and south china as a quasi rigid block around a pole north of the stanovoy belt which rules out the existence of an amurian plate as previously defined and implies 2 mm yr 1 of left lateral slip on the qinling shan fault zone

alteration zonation and short wavelength infrared swir characteristics of the honghai vms cu zn deposit eastern tianshan nw china abstract the honghai vms cu zn deposit is located in the dananhu tousuquan arc eastern tianshan northwestern china orebodies of the honghai deposit are buried 300 m underground and hosted by the middle ordovician upper silurian daliugou formation felsic to intermediate volcanic sedimentary rocks at the footwall and hanging wall of the massive sulfide lens intensive and pervasive phyllic alterations were found detailed drill core logging petrographic study and electron microprobe analyses had delineated six alteration mineralization zones namely from top to bottom zone i chlorite albite white mica carbonate ii epidote chlorite albite white mica carbonate iii quartz white mica pyrite iv massive sulfide v chlorite pyrite white mica and vi chlorite quartz white mica our new data supported the sub seafloor replacement influence for the honghai vms deposit as evidenced by the presence of 1 sulfide breccias in the immediate host rocks 2 rapid emplacement of host rocks 3 strong phyllic alteration in the immediate hanging wall 4 replacement textures of the massive sulfides 5 barite as gangue minerals moreover intensive chlorite and epidote alterations and vein mineralization are present in the hanging wall which are comparable with porphyry related propylitic alteration besides different mineralogy and mineral chemistry are present between chlorites from the hanging wall and footwall at honghai which probably suggested porphyry style alteration and mineralization overprinting at honghai short wavelength infrared swir spectral analysis had identified mainly white mica chlorite and epidote and minor montmorillonite calcite gypsum kaolinite and prehnite the wavelengths of the aloh absorption feature for white mica range from 2194 to 2221 nm suggesting compositions from paragonite through muscovite to phengite the wavelengths of feoh absorption feature for chlorite range from 2249 to 2261 nm indicating compositions from mg rich to fe rich chlorite according to swir measurements and electron microprobe analyses empa areas proximal to the massive sulfides are characterized by short wavelength of the aloh absorption feature and high alvi content of white mica petrography and empa showed that chlorite in the ore proximal zones are more mg rich than that in ore distal zones these findings indicated high temperature for the white mica formation and more seawater influx during the chlorite formation in areas near the massive sulfides this study suggested that swir analysis supported by petrographic study and empa can serve as an effective tool in alteration mapping and mineral geochemical variations are potential deposit scale exploration vectoring tools

vertical extrusion and horizontal channel flow of orogenic lower crust key exhumation mechanisms in large hot orogens a large database of structural geochronological and petrological data combined with a bouguer anomaly map is used to develop a two stage exhumation model of deep seated rocks in the eastern sector of the variscan belt an early sub vertical fabric developed in the orogenic lower and middle crust during intracrustal folding followed by the vertical extrusion of the lower crustal rocks these events were responsible for exhumation of the orogenic lower crust from depths equivalent to 18 20 kbar to depths equivalent to 8 10 kbar and for coeval burial of upper crustal rocks to depths equivalent to 8 9 kbar following the folding and vertical extrusion event sub horizontal fabrics developed at medium to low pressure in the orogenic lower and middle crust during vertical shortening fabrics that record the early vertical extrusion originated between 350 and 340 ma during building of an orogenic root in response to se directed saxothuringian continental subduction fabrics that record the later sub horizontal exhumation event relate to an eastern promontory of the brunia continent indenting into the rheologically weaker rocks of the orogenic root indentation initiated thrusting or flow of the orogenic crust over the brunia continent in a north directed sub horizontal channel this sub horizontal flow operated between 330 and 325 ma and was responsible for a heterogeneous mixing of blocks and boudins of lower and middle crustal rocks and for their progressive thermal re equilibration the erosion depth as well as the degree of reworking decreases from south to north pointing to an outflow of lower crustal material to the surface which was subsequently eroded and deposited in a foreland basin indentation by the brunia continental promontory was highly noncoaxial with respect to the se oriented saxothuringian continental subduction in the early visean suggesting a major switch of plate configuration during the middle to late visean

short wavelength infra red swir characteristics of hydrothermal alteration minerals in skarn deposits example from the jiguanzui cu au deposit eastern china abstract the jiguanzui cu au deposit is an important skarn deposit in the edong ore district of the middle lower yangtze river valley metallogenic belt mlyrb eastern china the mineralization occurred dominantly in the lower middle triassic jialingjiang formation marble either along interlayer fracture zones or along the intrusive contact with the early cretaceous quartz diorite based on the mineral assemblages and textural relationships the jiguanzui alteration mineralization can be divided into five stages namely i prograde skarn alteration garnet pyroxene ii retrograde alteration hornblende epidote actinolite iii hematite mineralization iv quartz sericite pyrite chalcopyrite mineralization main cu au mineralization stage and v calcite sulfide mineralization pyrite chalcopyrite molybdenite galena sphalerite systematic short wavelength infrared swir spectral analyses show that alteration minerals at jiguanzui include mainly sericite group minerals montmorillonite illite and muscovite kaolinite and carbonate minerals calcite ankerite and dolomite with minor chlorite halloysite and dickite spectral features of stage iv sericite group minerals indicate that the al oh absorption feature wavelength positions pos2200 have shifted toward longer wavelengths 2209 nm in the ore proximal area which may be caused by the substitution of fe and mg in the octahedral al site the vertical distance of mineralization indication can reach up to ca 450 m but can be affected by the wall rock lithology and the jiguanshan fault zone the fe oh absorption feature wavelength positions pos2250 of chlorite in the middle triassic puqi formation hornfels have also shifted toward longer wavelengths in the ore proximal area which may be caused by the relative mg rich nature of the chlorite we conclude that the high pos2200 2209 nm of sericite group minerals and the high pos2250 of chlorite can be used as prospecting tools for the jiguanzui cu au skarn mineralization

evaluation of inter instrument variations among short wavelength infrared swir devices in this study we investigate the inter instrument variation of the alunite 1 480 nm oh overall range 1 475 1 498 nm and the white mica al oh overall range 2 186 2 225 nm spectral absorption features by measuring the same sets of samples using two devices of each of the three major types of portable swir instruments portable infrared mineral analyzer pima terraspec and portable near infrared spectrometer pnirs all instruments have good short term reproducibility the arc centre of excellence in ore deposits codes pima was assessed for long term reproducibility and it was found to be stable with 0 to 1 nm variations over at least seven years there are differences in the results measured by different instruments even of the same type the pima instrument from the economic geology research unit generates alunite results 1 to 2 nm lower than those of the codes pima the two terraspec instruments used in this study produced results very similar to each other mostly with 0 to 1 nm differences in alunite 1 480 nm spectral absorption measurements but the results are 1 to 3 nm lower than those of the codes pima the two pnirs devices generated results that differed from each other by 1 to 4 nm mostly with 2 to 3 nm differences in alunite measurements compared with the pima results one pnirs dataset is very similar with 0 to 1 nm differences whereas the other pnirs dataset is 0 to 5 nm off mostly with 3 nm differences in alunite measurements the white mica al oh spectral absorption feature wavelength measurements are more similar among the instruments with the maximum difference being 2 nm despite the differences in absolute values the ranking of the samples in those datasets for the two tested parameters is largely the same which indicates that all the instruments will produce datasets showing the same trends the implication is that one project should use the same instrument for all the measurements if another instrument has to be used or the original instrument is repaired or tuned it is suggested that a set of samples covering most of the variation range should be measured with both instruments to evaluate the inter instrument variation and to establish a correction formula to keep consistency in the database 2012 by economic geology inc

paleomagnetism of paleozoic and mesozoic sediments from the southern margin of mongol okhotsk ocean far eastern russia 1 this paper presents new data from paleomagnetic investigations of middle paleozoic early middle late devonian early carboniferous and middle jurassic geological units from the amuria block south of the mongol okhotsk suture zone with fold tests for all localities and two polarities for the devonian our new results constrain the evolution of the mongol okhotsk ocean from the devonian to the middle jurassic the corresponding paleopoles lie at 21 6 n 6 3 e dp dm 5 3 10 6 for early devonian 26 3 n 345 3 e dp dm 6 4 12 8 for early middle devonian 24 6 n 12 9 e dp dm 8 7 16 9 for middle late devonian 40 5 n 352 4 e dp dm 9 16 7 for late devonian 39 8 n 31 6 e dp dm 10 15 5 for early carboniferous and 46 n 37 9 e dp dm 9 4 13 4 for middle jurassic the poles confirm that the large paleozoic mongol okhotsk ocean closed during the jurassic ending up in the late jurassic or early cretaceous at the eastern end of the suture zone as originally proposed on geological grounds the new paleomagnetic results exhibit large tectonic rotations about local vertical axes which we interpret as probably arising from both the collision process and left lateral shear movement along the suture zone related to incipient extrusion of amuria due to indentation of india into asia

mesozoic paleomagnetic results of the tarim craton tertiary relative motion between china and siberia paleomagnetic poles from two late jurassic to late cretaceous stratigraphic sections on the northern boundary of the tarim craton in western china are concordant with poles of similar age from eastern china when combined with previously published data these new results suggest that the major tectonic blocks which comprise china the tarim yangtze and sino korean cratons have been arranged in approximately their present relative configuration since cretaceous times the averaged cretaceous paleomagnetic pole for china is significantly different from the averaged cretaceous pole for siberia the difference may reflect significant relative post cretaceous motion between the composite china terrane and the siberian craton alternatively the cretaceous pole for siberia may not be reliable

left lateral sense offset of upper proterozoic to paleozoic features across the gobi onon tost and zuunbayan faults in southern mongolia and implications for other central asian faults abstract we present a preliminary study of upper proterozoic to paleozoic features adjacent to and offset across three faults in southern mongolia restoration of four offset stratigraphic units adjacent to the gobi onon fault indicates a left lateral sense offset of 70 95 km the tost fault has a left lateral sense offset of 95 125 km defined by three offset features the zuunbayan fault has seven offset features that display left lateral sense offsets of 185 235 km deformation on these faults apparently occurred during the mesozoic prior to the late cretaceous based upon the age of offset features the age of overlap sequences and inferred timing relationships with regional contractional structures although cenozoic overprinting and reactivation has occurred along parts of these faults thus complicating their restorations we present a testable hypothesis which predicts possible connections between these faults and faults within china

structure and petrology of the altan uul ophiolite new evidence for a late carboniferous suture in the gobi altai southern mongolia altan uul and nemegt uul are mountain ranges in southern mongolia containing polydeformed mid to late palaeozoic sedimentary volcanic and metamorphic rocks uplifted at a restraining bend along the gobi tien shan left lateral strike slip fault system altan and nemegt uul contain part of an intra oceanic island arc that was active during the carboniferous thrust bound sequences of highly fractured pillow basalt cumulate gabbro peridotite serpentinite and jasperoid occur directly north of the arc rocks in at least three discrete belts and are interpreted to be fragments of an ophiolite metamorphosed marine sediments that have undergone intense contractional strain lie north of and structurally below the ophiolitic rocks the gabbros within the ophiolitic sequences have undergone prograde metamorphic reactions consistent with an ocean floor environment and trace element analyses are similar to those from cumulate gabbros of the oman ophiolite combined field and petrological evidence suggests that there is an east west trending south dipping late carboniferous suture in altan and nemegt uul that may be regionally correlated in the southern gobi altai region this proposed suture represents a new and important tectonic boundary between tectonostratigraphic terranes in southern mongolia requiring modification of existing models of late palaeozoic terrane accretion in the central asian orogenic belt

evolution of the subseafloor hydrothermal system associated with the ming vms deposit newfoundland appalachians and its controls on base and precious metal distribution the 487 ma ming volcanogenic massive sulfide vms deposit consists of four subparallel elongated semi massive to massive sulfides lenses the 1807 1806 ming north and ming south zones hosted in rhyodacite of the rambler rhyolite formation newfoundland appalachians a discordant cu rich lower footwall zone underlies the semi massive to massive sulfide lenses alteration associated with mineralization can be divided into nine facies that formed in three paragenetic stages 1 weak quartz calcite spessartine quartz sericite and quartz sericite chlorite alteration stage 1 2 quartz chlorite quartz chlorite sulfide and quartz chlorite sericite assemblages stage 2 and 3 quartz sericite sulfide and localized mn rich carbonate assemblages stage 3 a thin syngenetic silica rich layer immediately overlies part of the vms deposit and likely formed during the early stages the volcanic architecture and synvolcanic faults controlled the lateral distribution of extrusive rocks and hydrothermal alteration precipitation of the high temperature discordant to semi conformable cu rich chloritic assemblages stockwork was laterally restricted to one of these synvolcanic faults and the transition from coherent to volcaniclastic dominated lithofacies lower temperature sericitic assemblages stages 1 and 3 are controlled by the distribution of volcaniclastic rocks and generally form the immediate footwall to the semi massive to massive sulfide lenses lithogeochemical mass balance calculations illustrate the alteration minerals and mineralization chlorite rich assemblages gains in sio2 fe2o3t mgo cr ni and cu and losses in na2o mno and cao and sericite rich assemblages gains in k2o zn and ag and losses in mno mgo cao na2o and y calcium and magnesium rich alteration assemblages are restricted to the northwest fringe of the deposit distal to the main chloritic and sericitic alteration and have elemental gains in p2o5 y and losses in k2o the late stage 3 quartz sericite sulfide assemblage overprints most assemblages hosts sphalerite galena sulfosalt ag au rich veins and is spatially associated with coherent volcanic rocks the less permeable nature of these rocks is interpreted to have acted as a physical barrier for ascending metal rich hydrothermal fluids results from the detailed reconstruction of the hydrothermal architecture and paragenetic evolution of the ming deposit suggest that precious metals were introduced during the waning stage of the hydrothermal system associated with decreases in temperature and ph of the hydrothermal fluids

reflectance spectroradiometry applied to a semi quantitative analysis of the mineralogy of the n4ws deposit carajas mineral province para brazil abstract quantifying the abundance and physicochemical properties of minerals using reflectance spectroradiometry in the visible near infrared and shortwave infrared 400 2500 nm regions is an important tool in mineral exploration in this study the reflectance spectra of drill cores from the world class n4ws iron deposit located in the carajas mineral province brazil were obtained these spectra were validated using x ray fluorescence xrf geochemical analyses and thin sections the reflectance spectra were collected using a fieldspec 3 spectroradiometer asd boulder colorado usa in 10 drill cores the mineralogy of the deposit is mainly hematite with lesser amounts of magnetite goethite quartz kaolinite gibbsite smectite talc carbonate and chlorite the mineralogy of the iron deposit was extracted from the spectral data using the geometry depth and wavelength of absorption features across the reflectance spectrum removed from the continuum the depth of the absorption features is proportional to the mineral abundance and the wavelength is proportional to the mineral chemical composition the diagnostic absorption features of each mineral were used to determine the mineral abundance and composition the final products include the abundance of iron hydro oxide 11 6 root mean square error rmse fe2o3 abundance of aluminous clays rmse 6 al2o3 abundance of talc 8 rmse mgo identification of clay type kaolinite montmorillonite or gibbsite composition of carbonate dolomite vs calcite and composition of chlorite mg vs fe the mineral abundance and composition results provided an effective characterisation of the ore protore and host rocks and showed variations within the ore body

strain distribution and fabric development modeled in active and ancient transpressive zones 1 a model based on kinematics of transpression allows the measurable internal parameters simultaneous strain fabric and vertical elevation to be simulated in relation to the macroscopically determined external parameters of transpressive zones i e zone width velocity angle of convergence and zone depth we present a diagram of convergence angle against time for homogeneous transpression where isolines of strain intensity d strain symmetry k and vertical elevation of rock samples are superposed however the distribution of internal strain parameters is sensitive to three types of strain partitioning 1 discrete partitioning results in general decrease of finite strain accumulations and in increase of pure shear component 2 ductile partitioning splits the transpressional domain into a pure shear zone where strain accumulations decreases and in a wrench dominated zone where strain accumulations increases and 3 viscosity partitioning is marked by different strain rates in zones of different viscosity and therefore by different strain parameters

late quaternary history of a mediterranean temporary pool from western morocco based on sedimentological and palynological evidence abstract using sedimentological and pollen analysis a reconstruction is presented here for the origin and history of a temporary pool from the quartzitic sandstone benslimane plateau w morocco the pool is one of many that originated from the dismantling of a past hydrographical network dated to the end of the lower pleistocene infilling of the pool began only recently between 5000 and 4000 cal bp and probably was in response to neolithic induced degradation of the regional vegetation cover the almost continuous pollen occurrence of isoetes velata type myriophyllum alterniflorum and ranunculus type throughout the palynological sequence indicates that the organisation of local plant communities in concentric belts a central aquatic community an intermediate amphibious one and a peripheral terrestrial one has remained unchanged since the mid holocene the stability of the vegetation structure and composition over more than 4000 years confirms the adaptation of the hydrophytic communities to human induced disturbances mainly grazing the long term pool longevity is attributed to an equilibrium between wind erosion and sedimentation the sediment accumulation balance that was null or negative during most of the pleistocene became positive under the influence of neolithic activities which may also be linked to unfavourable climatic conditions these results have important implications for the long term conservation of biodiversity as these rare habitats are rapidly declining since temporary pools also protect the quartzitic sandstone plateau from erosion their disappearance could trigger the reorganisation of the hydrological network and the resumption of soil erosion

a multi sensor logger for rock cores methodology and preliminary results from the matagami mining camp canada abstract diamond drilling typically constitutes a major part of costs in advanced mineral exploration programs this generates thousands of meters of rock cores during major exploration campaigns but the cores are not currently utilized to their full potential they could supply three dimensional information on physical properties geochemistry and mineralogy such data could be used to model the geology or physical properties in 3d characterize hydrothermal alteration or provide chemo stratigraphic constraints for example but measuring all the parameters one by one at high spatial resolution by traditional methods would be impractical due to cost or time considerations and for some parameters it would destroy the core e g geochemistry in this paper we describe a multi sensor core logger and its use on rock cores from exploration diamond drill holes this semi automated system can measure near simultaneously non destructively and at high spatial resolution the following parameters 1 volumetric magnetic susceptibility 2 density using gamma ray attenuation 3 several chemical elements through energy dispersive x ray fluorescence spectrometry and 4 visible near infrared spectrometry which allows numerous minerals to be detected and characterized the logger also acquires a continuous image of the core using a line scan camera which allows the user to compare other properties with the visual aspect of the core and creates a complete virtual archive the aim of this mostly methodological paper is to describe the logger as a whole and then each instrument or sensor separately outlining the numerous tests that have been performed to assess and improve data quality we also present preliminary results from the matagami mining camp of canada a base metal district

volcanic influences on hydrothermal and diagenetic alteration evidence from highway reward mount windsor subprovince australia synvolcanic sills and cryptodomes hosting the highway reward volcanic hosted massive sulfide deposit invaded wet poorly consolidated silt sand and pumice breccia margins of the porphyriric units display perlitic and quench fractures suggesting that they were formerly glassy interiors of the rhyolites rhyodacites and dacites were originally glassy partly glassy or comprised crystalline domains exhibiting spherulitic lithophysae and micropoikilitic textures no glass is preserved and the sills and cryptodomes are now completely crystalline primary devitrification structures crystallized early above the glass transition temperature and before the formarion of perlite or quench fractures crystallization of residual glass proceeded by diagenetic alteration volcanic associated hydrothermal alteration and ore associated hydrothermal alteration massive sulfide ore is enclosed in a discordant alteration envelope that extends at least 60 m above ore and is known to a depth of 150 m in the footwall in general there is a progression from central quartz sericite pyrite zones giving way to zones of chlorite n anhydrite n gypsum chlorite sericite quartz and finally chloritesericite distal to ore the outermost alteration grades into ithofacies that have altered to various background assemblages of feldspar hematite sericite chlorite quartz epidote and carbonate compared to least altered lithofacies the quartz sericite pyrite zones are enriched in sion k20 fe o3 s and ba and depleted in n o cao mgo and sr elevated concentrations of mgo fe203 and s coupled with low na o cao and k o values characterize chlorirized zones the pattern of low n o cao and mgo values and high k o values passing outward through the chlorite sericite n quartz zones is more erratic the ishikawa alteration index ai value and the chlorite carbonate pyrite index ccpi value become progressively larger passing from background altered facies ai 60 ccpi 20 55 into the footwall and hanging wall alteration zones ai 89 97 ccpi 41 99 at ai values greater than 90 cu bi and mo are elevated the s n o ratio increases toward ore whereas sr ba ratios are lowest at ai values above 90 the geochemical halo patterns reflect the composite response of lithofacies to mineralogical and textural chan es accompanying diagenetic alteration volcanic associated hydrothermal alteration and ore associated hydromermal alteration most alteration zones around ore display two or more overprinting alteration mineral assemblages within single alteration zones the distribution of alteration minerals and assemblages varies spatially in response to contrasring lithofacies character formerly glassy coherent and volcaniclastic facies display mineralogical and textural changes that reflect the influence of fracture perlitic quench and or matrix permeability and porosity on fluid migration crystalline domains of volcanic facies generally preserve their original texture although recrystallization has partly destroyed primary devitrification microstructures alteration minerals are localized along cooling joints hydraulic fractures and veins or form mottled patchy or wispy domains in contrast siltstone that separates intrusions and forms the matrix in peperite is relatively unaltered or was baked during magma sediment mixing in zones of intense quartz sericite n pyrite chlorite n anhydrite gypsum and sericite alteration high water rock ratios an extended history of fluid flow and elevated temperatures promoted large scale mobilization of elements in all facies relics of the early alteration mineral assemblages are locally preserved in these zones and imply a progression from initial volcanic determined

near infrared effectiveness on degraded core in tropical climates in tropical climates postdrilling oxidation of sulfide rich core can severely degrade drill core producing low temperature iron oxyhydroxides sulfates and clays variable growth of these secondary minerals in exposed drill core combined with the hydration and degradation of primary hydrothermal minerals may lead to the production of spurious results in near infrared nir spectroscopic studies however the nir technique can remain an effective tool in assessing hydrothermal alteration even in extremely degraded core we have assessed the usefulness of the nir technique on degraded core at the ladolam gold deposit papua new guinea here we seek to determine whether the primary alteration mineralogy had been significantly transformed by postdrilling oxidation over several years of weathering in doing so the study tested whether nir analysis can be an effective tool in the discrimination of primary hydrothermal minerals in degraded core our study was made possible using semiquantitative x ray diffraction qxrd analyses of a drill hole in 2004 where samples were collected at 50 m intervals we subsequently repeated nir and qxrd analyses on the same drill core in 2012 after nine years of storage the drill core had degraded considerably with the growth of jarosite and other sulfates despite this xrd results from 2004 and 2012 show no major differences in the primary alteration mineralogy closely spaced nir analyses were conducted at 1 m intervals to increase the chance of obtaining a spectrum of the primary mineralogy and to exclude secondary oxidation minerals the drill core where possible was broken immediately prior to analysis to obtain a fresh surface on average over a 10 m interval approximately 25 of the nir spectra did not contain secondary minerals and relict primary alteration minerals could be detected the remaining spectra were affected by the occurrence of secondary jarosite gypsum and or residual water but in most cases the primary alteration mineralogy could be determined we conclude that nir analyses remain an effective tool in the construction of geological deposit models when logging degraded historic core even for sulfide rich core that has degraded in tropical environments

phyllic alteration and the implications of fluid composition at the copper flat hydrothermal system new mexico usa abstract the copper flat hydrothermal system in hillsboro new mexico usa is hosted by a partially brecciated porphyritic quartz monzonite intrusive body igneous rocks are alkaline to calc alkaline and chondrite normalized rare earth element ree plots show enrichment in rees that is consistent with other regional laramide igneous rocks five assemblages of weak to moderate intensity phyllic alteration with distinct paragenetic relationships exist at the deposit and are classified as early phyllic quartz sericite pyrite qsp sericite quartz sericite carbonate and late qsp carbonate is common and is part of some phyllic and the potassic alteration assemblages carbonates and phyllosilicates were analyzed by electron microprobe white micas show substantial substitution of al by fe and mg and secondary biotite is mg rich relative to other porphyry cu systems the micas from copper flat contain on average greater f carbonates from veins and the replacement of mafic silicates and feldspars were determined to be mostly calcite but reduced metal carbonates such as ankerite and rhodochrosite are also present in the alteration assemblages the fluid s responsible for alteration are inferred to be co2 rich and ph neutral as interpreted from the widespread presence of carbonates in both the potassic and phyllic alteration zones and the white mica composition carbonate mineral compositions and absence of sulfates in the potassic alteration suggest that the hydrothermal fluids were not highly oxidized and were sulfur poor these features of alteration and geochemistry at copper flat are atypical of most porphyry cu mo deposits in the southwestern u s and may be more characteristic of porphyry cu au and porphyry mo deposits

north luzon and the philippine sea plate motion model insights following paleomagnetic structural and age dating investigations results of one of the most comprehensive paleomagnetic and supporting geological programs ever carried out in offshore se asia on north luzon northern philippines are reported six new results based on 66 sites are reported from a total collection of 243 individual sites declinations in the data subset are sometimes scattered likely reflecting combinations of major plate and local rotations in both clockwise and counterclockwise directions and thus have a somewhat limited value for tectonic modeling the inclination data are however much more valuable and can be best explained if north luzon traveled as part of the philippine sea plate for most of its history a scenario which is compatible with the known geology of the eastern philippines and broader region in the proposed model for all of its eocene pliocene history north luzon is placed on the western edge of the philippine sea plate effectively always just to the west of the site where the benham plateau formed 40 ma the paleomagnetic data indicate a substantial northward migration of the area since the start of the neogene with an earlier interval stretching back to at least the mid early cretaceous when this part of the plate occupied equatorial latitudes post 15 ma motion of the plate has involved the indentation of the palawan microcontinental block into the western side of the philippine archipelago deformations induced by this process offer the most likely explanation for the scattered declinations observed in north luzon and areas a short distance to the south

the south siberia central mongolia transect abstract studies of geological and geophysical data on the south siberia central mongolia geoscience transect which runs approximately along 100 e show that the asian continent was formed in the phanerozoic by accretion of terranes most of which were microcontinents with precambrian basement suture zones separating the terranes are deformed and deeply eroded magmatic arcs of different widths likewise classified as specific terranes in these sutures magmatic arc rocks are locally associated with fore and back arc basin series most of the oceanic crust has been subducted the observed ophiolite belts are as a rule attributed to the base of oceanic island arcs the fragment of the asian continent traversed by the transect was formed through early middle and late paleozoic stages of accretion

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

late cenozoic transpression in southwestern mongolia and the gobi altai tien shan connection the gobi altai region of southwestern mongolia is a natural laboratory for studying processes of active transpressional intracontinental mountain building at different stages of development the region is structurally dominated by several major e w left lateral strike slip fault systems the north gobi altai fault system is a seismically active right stepping left lateral strike slip fault system that can be traced along the surface for over 350 km the eastern two thirds of the fault system ruptured during a major earthquake m 8 3 in 1957 whereas degraded fault scarps cutting alluvial deposits along the western third of the system indicate that this segment did not rupture during the 1957 event but has been active during the quaternary the highest mountains in the gobi altai are restraining bend uplifts along the length of the fault system detailed transects across two of the restraining bends indicate that they have asymmetric flower structure cross sectional geometries with thrust faults rooting into oblique slip and strike slip master faults continued ne directed convergence across the fault system coupled with left lateral strike slip displacements will lead to growth and coalescence of the restraining bends into a continuous sublinear range possibly obscuring the original strike slip fault system this may be a common mountain building process the largely unknown gobi tien shan fault system is a major left lateral strike slip fault system 1200 km long that links the southern ranges of the gobi altai with the barkol tagh and bogda shan of the easternmost tien shan in china active scarps cutting alluvial deposits are visible on satellite imagery along much of its central section indicating quaternary activity the total displacement is unknown but small parallel splays have apparent offsets of 20 km suggesting that the main fault zone has experienced significantly more displacement field investigations conducted at two locations in southwestern mongolia indicate that late cenozoic transpressional uplift is still active along the fault system the spatial relationship between topography and active faults in the barkol tagh and bogda shan strongly suggests that these ranges are large coalescing restraining bends that have accommodated the fault s left lateral motion by thrusting oblique slip displacement and uplift thus from a mongolian perspective the easternmost tien shan formed where it is because it lies at the western termination zone of the gobi tien shan fault system the gobi tien shan fault system is one of the longest fault systems in central asia and together with the north gobi altai and other smaller subparallel fault systems is accommodating the eastward translation of south mongolia relative to the hangay dome and siberia these displacements are interpreted to be due to eastward viscous flow of uppermost mantle material in the topographically low e w trending corridor between the northern edge of the tibetan plateau and the hangay dome presumably in response to the indo eurasian collision 2500 km to the south

short wavelength infrared swir spectroscopy of phyllosilicate minerals from the tonglushan cu au fe deposit eastern china new exploration indicators for concealed skarn orebodies abstract the middle lower yangtze river metallogenic belt mlyrb is one of the most important cu au fe mo skarn porphyry metallogenic belts in eastern china after several decades of mining the shallow level mineral resources have been gradually exhausted which call for new exploration tools for concealed orebodies the tonglushan cu au fe skarn deposit 86 3 mt 1 66 cu 0 94 g t au and 39 4 fe is located in the western mlyrb skarn alteration mineralization are mainly hosted in the contact zone between cretaceous 141 ma quartz monzodiorite and its porphyry and the lower triassic carbonate rocks based on the mineral assemblages and their macro microscopic textural relationships the tonglushan cu au fe mineralization alteration can be divided into five stages pre ore s1 skarn potassic alteration fe ore s2 retrograde alteration and fe oxides cu au ore s3 quartz sulfides carbonate alteration s4 and supergene alteration s5 apart from the major skarn and retrograde alteration and carbonate minerals abundant fine grained phyllosilicate minerals including chlorite white mica illite muscovite and phengite smectite montmorillonite and saponite and kandite kaolinite dickite and halloysite group minerals have been identified at tonglushan by swir spectrometry integrating petrographic observations and swir spectral analysis four alteration zones with distinct phyllosilicate assemblages have been distinguished from the intrusion outward i ore barren quartz monzodiorite and its porphyry montmorillonite illite chlorite ii endoskarn close to the skarn hydrothermal mineralization center montmorillonite illite chlorite kaolinite dickite iii skarn hydrothermal mineralization center saponite chlorite and iv the external contact zone in dolomitic marble montmorillonite chlorite kaolinite dickite for the tonglushan altered rock samples swir spectrometry has identified wavelength shifts in the fe oh al oh and sub al oh absorption features of chlorite white mica montmorillonite and kandite respectively chlorite fe oh absorption occurs at longer wavelengths 2 250 nm white mica montmorillonite al oh absorption occurs at unusually long 2 212 nm and short 2 170 nm in strongly altered skarn proximal samples moreover the presence of kaolinite dickite saponite actinolite phlogopite and or chlorite quartz sulfides veins in these samples can be used as new vectors to explore deep level mineralization centers at tonglushan the distribution of various kinds of phyllosilicate alteration minerals at tonglushan especially the white mica and kandites with higher crystallinity in the deep contact zones indicates that the neutral to acidic hydrothermal fluids may have been generated with the precipitation of fe oxides and sulfides this study also highlights the potential of swir spectroscopy of phyllosilicate minerals for exploring concealed skarn orebodies in the mlyrb

reinterpretation of the active faulting in central mongolia we present remote sensing and fi eld observations of an 350 km long east west left lateral strike slip fault the south hangay fault in the hangay mountains of central mongolia an area previously believed to be deforming solely by slip on scattered and randomly oriented normal faults the known dip slip faults are shown to be short segments introduced at bends in the much longer strike slip fault our observations show that the active faulting in the hangay mountains is consistent with the regional strain fi eld of mongolia and does not require as suggested in other studies that the faults result from stresses introduced by the locally elevated topography our observations help to defi ne the active tectonics of this important part of the india eurasia collision the south hangay strike slip fault is a potential source of large magnitude earthquakes and constitutes a previously unrecognized hazard in this part of mongolia

rapid mineralogical and geochemical characterisation of the fisher east nickel sulphide prospects western australia using hyperspectral and pxrf data abstract the use of shortwave infrared swir and thermal infrared tir hyperspectral data in mineral exploration has been well documented in many mineralisation types but is limited in komatiite hosted nickel sulphide deposits this project combines hyperspectral portable x ray fluorescence pxrf and whole rock geochemical data to assess different analytical techniques in the exploration of these deposits we use the fisher east nickel sulphide prospects western australia for our case study the fisher east prospects lie in an area of the eastern goldfields that has historically been underexplored and understudied the rocks have undergone intense deformation with primary igneous textures being destroyed along with strong alteration to talc carbonate assemblages combining different analytical tools allowed for differentiation of a and b zones of original komatiite flows and the reconstruction of original volcanological facies in a setting where whole rock chemistry as well as igneous textures have been substantially modified by metamorphism by using different lithogeochemical techniques including pxrf this study shows the fisher east prospects are hosted within channelised komatiite flows and have similar characteristics to kambalda style deposits

middle cambrian to permian subduction related accretionary orogenesis of northern xinjiang nw china implications for the tectonic evolution of central asia abstract middle cambrian to permian subduction related records are widely distributed in northern xinjiang which can be grouped into the chinese altay east junggar eastern tien shan west junggar yili and tarim domains by integrating paleogeographic and geological data we suppose that the chinese altay east junggar eastern tien shan domain was more closely located to siberia while the west junggar and yili domains occupied an intermediate position near the kazakhstan block in the early paleozoic paleoasian ocean distribution of andean type magmatic arcs island arcs accretionary wedges ophiolitic slices and or microcontinents shows an archipelago paleogeography forming a huge accretionary active margin sequences the tarim domain was on the opposite side of the early paleozoic paleoasian ocean remaining passive margin these tectonic units drifted northwards and approached the southern active margin of the siberian craton in the late paleozoic leading to termination of the paleoasian ocean and formation of a complicated orogenic collage between siberian craton and the tarim block between the end permian and triassic these multiple accretion processes significantly contributed to the lateral growth of central asia

upper silurian and devonian pelagic deep water radiolarian chert from the khangai khentei belt of central mongolia evidence for middle paleozoic subduction accretion activity in the central asian orogenic belt abstract recent mapping projects undertaken in central mongolia have revealed the widespread occurrence of radiolarian chert within a paleozoic accretionary complex we present the results of the first detailed tectonostratigraphic and radiolarian biostratigraphic investigations of the gorkhi formation in the khangai khentei belt of the central asian orogenic belt the gorkhi formation consists of sandstone shale alternating sandstone and shale of turbidite affinity and chert with small amounts of siliceous shale basalt limestone and clast bearing mudstone radiolarian chert that is completely devoid of terrigenous clastic material is commonly associated with underlying basalt sedimentary contact and with conformably overlying siliceous shale and turbidite deposits the tectonic stacking of basalt chert and chert turbidite successions is the most remarkable structural feature of the formation the recovery of moderately well preserved radiolarians and conodonts from red chert led to the recognition of four radiolarian assemblages that have a combined age range from the latest silurian pridolian to the late devonian frasnian no age control exists for the siliceous shale shale and sandstone although they are considered to be latest devonian or slightly younger on the basis of stratigraphic relationships with underlying chert the gorkhi formation has previously been interpreted as a thick sedimentary basin deposit overlying an unexposed archean neoproterozoic basement however the stratigraphy within individual tectonic slices clearly corresponds to that of an ocean plate stratigraphy of an accretionary complex generated by the trenchward movement of an oceanic plate from the lowermost to uppermost units the stratigraphy comprises ocean floor basalt pelagic deep water radiolarian chert hemipelagic siliceous shale and terrigenous turbidite deposits the biostratigraphic data obtained in the present study provide corroborating evidence for the existence of an extensive deep water ocean that enabled the continuous sedimentation of pelagic chert over a period of nearly 50 million years these data together with structural data characterized by tectonic repetition of the stratigraphy indicate that these rocks formed as an accretionary wedge along an active continental margin possibly that of the angara craton the mid oceanic chert was probably deposited in the northern hemisphere portion of the paleo pacific ocean that faced the angara craton and the north china tarim blocks thus we propose that subduction accretion processes along the paleo pacific rim played an important role in the accretionary growth of the active continental margin of the angara craton directly influencing the evolution of the central asian orogenic belt

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

the baganuur coal deposit mongolia depositional environments and paleoecology of a lower cretaceous coal bearing intermontane basin in eastern asia abstract the investigations involved geophysical sedimentological palynological chemical and mineralogical studies supported by field based infrared spectrometry the baganuur basin central mongolia is among the rift or pull apart basins which subsided at the boundary between the jurassic and the lower cretaceous in east asia during the berriasian peat accumulation began in the area under study in central mongolia the palynoflora is akin to the siberian palynological province based on the phytoclast assemblages and the ratios of total sulfur content to total organic content marine transgressions into this intermontane basin may be ruled out the coal interseam sediments were laid down prevalently under neutral to slightly alkaline conditions only in some carbonaceous sediments the ph of intrastratal solutions was lowered suboxic to anoxic conditions persisted during almost the entire lower cretaceous period in the baganuur basin based on the distribution of fining and coarsening upward sequences and the organic matter the basin fill has been subdivided into seven depositional units a fluvial swamp b fluvial lacustrine c deltaic fluvial d fluvial e fluvial deltaic lacustrine floodplain f lacustrine deltaic swamp g swamp fluvial a conspicuous change in the fluvial lacustrine regime and an increase in the sediment supply may be observed at the boundary between depositional units b and c a strong uplift triggered the onset of an intensive delta sedimentation lithoclasts heavy minerals e g apatite zircon garnet anatase brookite epidote sphene tourmaline and phyllosilicates e g kaolinite smectite mica chlorite attest to a mixing of detrital material one provenance area was abundant in acidic plutonic rocks as shown by the granitic lithoclasts the other in volcanic rocks which produced the vitroclastic debris deposited as tephra fallout post depositional alteration of the siliciclastic interseam sediments was favored by a distinctive facies association of transmissive and sealing horizons it led to a re deposition of ca u and sr in the siliciclastics post depositional alteration of the organic material converted it into lignite to subbituminous c coal

capturing digital data of rock magnetic gamma ray and ir spectrometry for in situ quality control and for the study of the physical chemical regime of residual kaolin deposits se germany abstract residual kaolin deposits are operated on a worldwide basis the majority of them is derived from chemical weathering of felsic rocks during the cenozoic this is true for the kaolin deposits on the western edge of the bohemian massif here this type of deposit provides industrial minerals for the ceramic industry in se germany this raw material formed under tropical climatic conditions during the miocene and pliocene across a vast peneplain only within the naab wondreb depression however were economic accumulations preserved from erosion here near tirschenreuth kaolin has been mined since its discovery in 1830 the semi consolidated regolith is composed of quartz and opaline material alkaline feldspar different types of kaolinite muscovite illite a variegated spectrum of 14 a phyllosilicates fe mn oxide hydroxides and minor heavy minerals mainly containing ti a precise determination of the mineralogical composition of the ceramic raw material has so far solely relied on laboratory techniques e g xrd xrf and spectroscopic methods to the contrary this study takes a different approach capturing digital data in the field to determine its mineralogical composition gamma spectrometry k u th measuring the susceptibility of and analyzing short wave infrared spectra allows for an in situ quality control of the run of mine raw material it further assists in mapping the monotonous lithology and enables the authors to constrain the physico chemical regime throughout formation of the kaolin deposit the benefit for technical mineralogy and applied economic geology and the strong points of capturing digital data in the field is the easy and cost efficient handling of the various methods methods that were applied in this way for the first time the in door calibration and test measurements as well as the data acquisition during the field survey are presented and the data are correlated with the enhancing or deteriorating impacts of the inferred minerals on the firing behavior of the ceramic product collecting digital data can also help constrain the physico chemical regime during formation of the argillaceous deposit and improve further exploration through fine tuning the genetic model of residual kaolin accumulation the late carboniferous granites around tirschenreuth underwent strong supergene alteration in the ph range of 2 5 7 at log a sio2 aq 2 5 to 3 5 which resulted in a thick kaolinitic regolith illite formed under slightly increased ph between 4 and 7 attests to a change from tropical to more temperate humid conditions in the area the chlorite group phyllosilicates and nontronitic members of the smectite group came into existence when the ph increased to a ph interval of 7 to 11 this considerable change in the ph of the meteoric solutions occurred at the end of the neogene between 4 55 ma and 3 99 ma the different field methods compensate for each others weak points neither method is successful on its own but the current configuration can easily be expanded to include additional methods as there are neutron and micro resistivity and air and space borne approaches to cover more swiftly a larger exploration or study area

finite strain calculations of continental deformation 2 comparison with the india asia collision zone numerical experiments on a thin viscous sheet model for deformation of continental lithosphere subjected to an indenting boundary condition yield distributions of crustal thickness of stress and strain rate and of latitudinal displacements that may be compared with observations in the india asia collision zone a simple indenting boundary condition applied to initially laterally homogeneous sheets obeying a power law rheology produces results that are in broad agreement with the observations provided that the power law exponent is three or greater and the sheet can support vertically integrated stress differences of 2 1013 5 1012 n m 1 in regions in front of the indenter under these conditions the calculated deformation shows accommodation of convergence primarily by crustal thickening to produce a plateau in front of the indenter palaeomagnetic data from india and tibet and the observed distribution of topography suggest that much of the post eocene convergence of india with asia has been taken up by deformation within asia that involved crustal thickening the principal difference between calculation and observation is the absence from the calculated strain rate fields of east west extension of the plateau in front of the indenting boundary the calculations show that once such a plateau is formed the buoyancy force associated with the crustal thickness contrast inhibits further thickening and the plateau strains at less than half the rate of its immediate surroundings seismically determined regional strain rates exhibit a similar distribution with the tibetan plateau straining at about one quarter the rate of the tien shan and ningxia gansu regions calculated principal compressive stress orientations and regional strain rates agree with the seismically determined quantities in the mongolia baikal tien shan tibet and ningxia gansu regions of asia to within the uncertainty of the latter the vertically integrated stresses that are calculated for the viscous sheet are comparable with those that can be supported by a theologically stratified continental lithosphere obeying laboratory determined flow laws we suggest that the thin viscous sheet model described in this paper and its companion gives a simple and physically plausible description of the observed deformation in central asia in this description the predominant mechanism of accommodation of continental convergence is diffuse crustal thickening with shear on vertical planes playing a subsidiary role once large crustal thickness contrasts have been established

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

alteration mineralogy at the cerro la mina epithermal prospect patagonia argentina field mapping short wave infrared spectroscopy and aster images the cerro la mina prospect located in the los menucos area argentina is currently being explored for epithermal gold mineralization triassic jurassic hydrothermal activity produced intense alteration of rhyolites andesites ignimbrites and tuffs of the late triassic los menucos group in the somun cura massif a detailed surface map of the principal alteration assemblages at cerro la mina was produced employing field mapping supported by short wave infrared swir field spectroscopy petrography x ray diffraction xrd and scanning electron microscopy sem advanced argillic argillic and silicic alteration zones and their internal mineral assemblage variations were recognized at cerro la mina the silicification consists of massive bodies of fine grained quartz and minor vuggy quartz locally containing disseminated aggregates of pyrite and rutile advanced argillic alteration of magmatic hydrothermal origin occurs adjacent to the silicic alteration zones and can be subdivided into three mineral assemblages 1 stage 1 alunite quartz dickite kaolinite pyrophyllite diaspore rutile pyrite barite 2 dickite kaolinite pyrophyllite diaspore pyrite barite and 3 dickite quartz diaspore the advanced argillic and silicic alteration grades to argillic alteration comprising three mineral assemblages 1 kaolinite dickite quartz illite smectite 2 kaolinite illite smectite ferroan clinochlore and 3 illite quartz muscovite kaolinite supergene alteration which locally overprints the prior alteration zones consists of jarosite hematite goethite stage 2 alunite aluminum phosphate sulfate aps poorly crystalline kaolinite consistent discrimination of the main alteration minerals of this prospect was also achieved by means of satellite multispectral remote sensing the application of image processing techniques specifically designed for mineral mapping to selected spectral bands of the terra aster multispectral sensor resulted in a detailed alteration map for the entire prospect comparison between the results achieved through remote sensing with field data on the cerro la mina confirmed the accuracy of the former the silicification and minor vuggy quartz the abundant dickite and the coarse grained hypogene alunite among other advanced argillic alteration assemblages suggest that cerro la mina corresponds to a volcanic hydrothermal leached environment possibly controlled by permeable lithological units these characteristics led us to interpret this prospect as a possible lithocap similar to those that typically host subsequent high sulfidation mineralization

zonation of alteration facies at western tharsis implications for the genesis of cu au deposits mount lyell field western tasmania the western tharsis deposit located in the mount read volcanic belt of western tasmania is one of 22 mainly cu au deposits in the mount lyell district although the orebody at western tharsis is characterized mainly by disseminated pyrite chalcopyrite like most other deposits in the mount lyell district it also contains bornite rich ores characteristic of a second less common type of deposit the deposit is stratiform and occurs within intermediate and felsic volcanic rocks of the 500 ma central volcanic complex alteration is developed broadly symmetrically around the ore zone with an ore bearing core characterized by a quartz chlorite sericite assemblage the core is enveloped by a quartz pyrophyllite topaz fluorite zunyite woodhouseite assemblage with local bornite bearing ore zones this zone in turn is enveloped by a pyritic quartz sericite assemblage the outermost quartz chlorite carbonate sericite albite assemblage is only developed in the stratigraphic footwall more than 200 m below the ore position the hypogene pyrophyllite bearing assemblage is more characteristic of high sulfidation than volcanic hosted massive sulfide vhms related alteration assemblages moreover the close relationship of this alteration assemblage with the more prevalent quartz chlorite sericite assemblage associated with disseminated pyrite chalcopyrite mineralization suggests that these two types of mineralization are two stages of one mineralizing event not the two separate events suggested by previous authors e g arnold and carswell 1990 geologic relationships and radiogenic isotope data are consistent with an ordovician 460 ma timing for mount lyell cu au mineral deposits this mineralization may be related to the geologic event that formed the local haulage unconformity these observations indicate a potential new exploration model for mineralization in the mount read volcanic belt and in surrounding ordovician rocks

palaeozoic terrane accretion in the western irish caledonides the southern boundary of the early caledonides in the british isles the dalradian supergroup is represented by the major highland boundary fair head clew bay line in the west of ireland accretion along this laurasian margin occurred by sinistral strike slip during two phases the earliest was responsible for the docking of the connemara terrane a displaced part of the dalradian outboard of the south mayo trough in the llanvirnian llandeilian this event is recorded independently by radiometrically dated sinistral strike slip deformation in the ox mountains of western ireland following deposition of a silurian overlap sequence sinistral movements were renewed between the upper llandoverian and the siegennian this event is part of a major phase of sinistral strike slip throughout the british isles involving accretion of the cadomian terrane and the devonian accretion of the avalon terrane in the northern appalachians

late permian paleomagnetic pole from dikes of the tarim craton china we have obtained a late permian paleomagnetic pole from dikes in the tarim craton of china directions of magnetization from 21 mafic and ultramafic dikes at three localities pass a fold test at the 95 confidence level the new paleomagnetic pole lies at lat 66 n long 181 e n 21 k 61 and 95 3 9 on the basis of a comparison with paleomagnetic data from adjacent tectonic units we conclude that 1 the late permian paleolatitude of the tarim craton differs from that of the sino korean craton suggesting that the two cratons were distinct tectonic units in late permian time 2 there was relative motion between the tarim craton and the siberian craton after late permian time and 3 negligible relative motions have occured between different thrust sheets in the keping bachu area of the north western tarim craton

age of palaeozoic granites and metamorphism in the tuvino mongolian massif of the central asian mobile belt loss of a precambrian microcontinent abstract the tuvino mongolian massif tmm was previously interpreted as a precambrian block within the central asian mobile belt according to this idea it consists of tectonic slices composed of metamorphic rocks of pre mesoproterozoic basement that experienced two episodes of regional metamorphism and mesoproterozoic cover rocks that were reworked together with the basement during high grade metamorphism zircon u pb dating of granitoids from all metamorphic complexes demonstrates that the earliest metamorphic event occurred at 536 6 ma significantly later than the deposition of the cover rocks regional upper amphibolite facies metamorphism which affected all metasedimentary units of the tmm occurred in the short time interval of 497 4 to 489 3 ma we propose that there is no simple basement cover relationship in the tuvino mongolian massif instead the massif consists of tectonic domains composed of heterogeneous metasedimentary successions with distinct pre metamorphic and pre tectonic histories that were juxtaposed by thrusting prior to 497 ma and then metamorphosed under upper amphibolite facies conditions we suggest that this thrusting event was associated with early palaeozoic collisional processes related to amalgamation of the central asian mobile belt our new model for the evolution of the tmm implies derivation of neoproterozoic terrigeneous metasediments from 800 900 ma granitoids formed in an andean type active continental margin setting

palaeostress reconstructions and geodynamics of the baikal region central asia part i palaeozoic and mesozoic pre rift evolution abstract this paper presents the first palaeostress results obtained for the basement of the baikal rift system in southern siberia russia large scale structural analysis and palaeostress reconstructions show that the palaeozoic mesozoic kinematic history precursor of the baikal cenozoic rifting is characterized by the succession of six regional palaeostress stages stress inversion of fault slip data and earthquake focal mechanisms is performed using an improved right dieder method followed by rotational optimization d delvaux tensor program the results are interpreted in the light of recent developments in the investigation of regional intraplate stress field and used as additional constraints for palaeogeodynamic reconstruction of central asia after the final palaeozoic closure of the palaeo asian ocean on the southern margin of the siberian platform the marginal suture with the sayan baikal caledonian belt was repeatedly and preferentially reactivated during the subsequent palaeozoic and mesozoic history this suture zone also controlled the opening of the baikal rift system in the cenozoic the progressive closure of the palaeo asian and mongol okhotsk oceans generated successive continental collisions which were recorded in the baikal area by brittle ductile and brittle deformations the first two palaeostress stages correspond to the successive collage of precambrian microcontinents and caledonian terranes along the southern margin of the siberian platform 1 late cambrian early ordovician n s compression and 2 late silurian early devonian nw se compression the next two stages are related to the remote effects of the complex evolution of the western palaeo asian ocean southwest of the siberian continent 3 late devonian early carboniferous n s compression recorded only in the altai region and 4 late carboniferous early permian e w compression recorded both in the altai and baikal regions the last stages are the consequences of the mongol okhotsk oceanic closure 5 late permian triassic nw se extension with development of cordilleran type metamorphic core complexes and volcanism along the active margin of the mongol okhotsk ocean 6 initial development of early middle jurassic 10 15 km wide molassic basins in trans baikal and large foredeeps along the southern margin of the siberian platform in probable extensional context but for which no palaeostress data are available and 7 final closure of the mongol okhotsk ocean in the cretaceous this last event results from the collision between the mongol china and the siberian plates and is evidenced by the inversion of the middle mesozoic basins and by late jurassic early cretaceous coal bearing sedimentation in trans baikal this long tectonic history yielded a highly heterogeneous basement in the baikal area precursor of the cenozoic rifting

chronological constraints on the pre orogenic history burial and exhumation of deep seated rocks along the eastern margin of the variscan orogen bohemian massif czech republic key lithological units of the high grade eastern margin of the bohemian massif were dated using the u pb and pb pb methods on zircons in order to establish a chronological framework for the geodynamic evolution of the variscan orogenic root the protolith ages for metagranitoids orthogneisses and granulites of thickened lower and middle crust reveal the existence of magmatic activity that occurred over a 100 million year time interval from cambro ordovician to early devonian times probably related to discontinuous intracontinental rifting of neoproterozoic crust our geochronological data suggest that the eastern part of the orogenic root represents thermally softened and rifted neoproterozoic crust preserved farther to the east as the brunia microcontinent zircon ages for felsic granulites high grade gneisses of the lower crust and of a syn convergence granodioritic intrusion in the upper crust indicate that thickening and exhumation of the crust occurred during a narrow time interval between 370 and 340 ma exhumation of the lower crust to mid crustal levels was a localized process that occurred at 340 ma and was associated with crustal scale folding in the internal part of the root as well as orogenic channel flow along the eastern collisional margin both types of exhumation mechanisms were driven by deep level wedging indentation of the easterly brunia continent followed by deposition of heavy minerals and pebbles derived from high pressure rocks in the adjacent foreland basin final orogenic development was characterized by ne sw dextral transpressive shearing parallel to the brunia margin as well as dextral trans tension associated with activity along the elbe lithospheric fault these processes affected the marginal parts of the orogenic root and were accompanied by 330 to 325 ma old syntectonic granitoid intrusions along reactivated lithotectonic boundaries rotation of the assembled orogenic belt accompanied by lithospheric faulting driven by westerly subduction roll back may be the most plausible model to explain late deformation of the orogenic root

re deciphering the tectonic jigsaw puzzle of northern eurasia abstract northern eurasia consists of the east european siberian north china and alai tarim cratons fragments of the supercontinent rodinia and the orogens of the baikalides timanides uralides altaids and mongolides these can be collectively classified as the central asian supercollage the baikalides and timanides host meso and neoproterozoic magmatic arc terranes that were sutured with the adjacent east european and siberian cratons in the end of the neoproterozoic the paleozoic part of the supercollage consists of three almost synchronous and subparallel neoproterosoic to paleozoic magmatic arc and turbidite superterranes as well as overlap assemblages bent into the world s largest oroclines analysis of their structural pattern supported by paleontological lithological and paleomagnetic data indicates that these superterranes might have been produced via formation of arc backarc systems at the margin of combined north china east european and siberian cratons and then deformed during paleozoic westward directed strike slip translation between the clockwise rotating siberian and eastward moving north china cratons it is proposed that this development took place against the respective breakup of the above mentioned cratons from the northern and southern margins of eastern europe in the neoproterozoic initially as a group of cratons called nena which reassembled in late paleozoic to early mesozoic times into laurasia part of the new supercontinent pangea in mesozoic cenozoic times the subduction related continental growth of northern eurasia continued in the nipponide kamchatka and kolyma alaska orogenic collages of the northern circum pacific which consist of paleozoic to cenozoic turbidite to island arc superterranes and overlap assemblages generally younging towards the pacific oceanic plate and also severely oroclinally bent it is proposed that terranes of the kolyma alaska and kamchatka collages were translated westward dextrally relative to siberia whereas nipponides were translated northward relative to north china similarly to the better constrained mesozoic cenozoic reconstructions of southeastern asia the two groups of collages started to collide along the mongol okhotsk suture zone in the south of the siberian craton in the end of the mesozoic and then continued to collide along the presently active plate boundary at the island of sakhalin the proposed scenario suggests similarities in paleozoic evolution of the central asian and mesozoic cenozoic evolution of the northern circum pacific supercollages both possibly formed in response to westward subduction and related strike slip translation of the paleo pacific oceanic plates the individual superterranes might have been consequently translated for as much as 4000 6000 km and oroclinally bent during such translation or and rotation of the adjacent cratons

late jurassic early cretaceous closure of the mongol okhotsk ocean demonstrated by new mesozoic palaeomagnetic results from the trans baikal area se siberia summary we present new palaeomagnetic results from the transba ikal area se siberia from the mongol okhotsk suture zone the boundary between the amuria and siberia blocks in order to better constrain the time of closure of the mongol okhotsk ocean in the mesozoic we col lected 532 rock samples at 68 sites in six localities of basalts trachy basalts and andesites from both sides of the mongol okhotsk suture at unda river j 3 51 7 n 117 4 e kremljevka peak k1 51 8 n 117 5 e and torey lakes k 1 50 1 n 115 9 e on the southern side of the suture and at monostoy river j 1 51 1 n 106 8 e ingoda river k 1 51 2 n 112 2 e and bichura town k 1 50 6 n 107 6 e on the northern side progressive thermal demagnetization enabled us to resolve low ltc and high htc temperature components of magnetization at most sites jurassic palaeopoles computed from the htcs show a large discrepancy with respect to the apparent polar wander path of eurasia which we interpret in terms of 1700 2700 km of post late jurassic northward movement of amuria with respect to siberia although ge ological data suggest a middle jurassic closure of the mongol okhotsk ocean in the west trans baikal region our data give evidence of a large remaining palaeolatitude difference between the amuria and siberia blocks in contrast early cretaceous sites cluster remarkably well along a small circle which is centred on the average site location this implies the absence of post early cretaceous northward motion of amuria relative to siberia and demonstrates the pre early cretaceous closure of the mongol okhotsk ocean finally we interpret the very large tectonic rotations about local vertical axes evidenced by the small circle distribution of poles as arising both from collision processes and from left lateral shear movement along the suture zone due to the eastward extrusion of amuria under the effect of the collision of india into asia

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

short wavelength infrared spectral characteristics of the hw horizon implications for exploration in the myra falls volcanic hosted massive sulfide camp vancouver island british columbia canada short wavelength infrared swir spectrometry has been used to identify previously unmapped hydrothermal alteration zones around volcanic hosted massive sulfide vhms orebodies at myra falls vancouver island british columbia hydrothermal alteration assemblages are uniformly dominated by fine grained white mica with poor development of mineralogical zonation swir spectrometry is an ideal exploration tool for characterizing this fine grained hydrothermal alteration at myra falls swir spectrometry has identified subtle shifts in the wavelengths of the aloh absorption feature of white mica corresponding to compositional changes in altered rhyolite distal and proximal to ore aloh absorption occurs at shorter wavelengths 2 198 nm and corresponds to lower fe fe mg and si al and higher na na k in strongly altered samples proximal to ore slightly sodic muscovites aloh absorption occurs at longer wavelengths 2 206 nm and corresponds to higher fe fe mg and si al and lower na na k in samples distal to ore nonsodic slightly phengitic muscovites white mica in siltstone within a meter of vhms ore has higher zn v fe and mg contents than white mica distal to these altered samples chlorite compositions identified by swir also show systematic changes with intensity of alteration and distance from ore the average wavelength of the feoh absorption feature for chlorite in rhyolitic samples proximal to ore is 2 241 nm intermediate mg chlorite whereas wavelengths in background samples average 2 247 nm intermediate fe chlorite similar changes are observed in footwall and hanging wall andesites with samples near the battle mine containing muscovite to phengitic muscovite average wavelength of the aloh absorption feature of 2 200 nm and mg rich chlorite average wavelength of the feoh absorption feature of 2 245 nm to regional andesite samples with phengitic muscovite average wavelengths of the aloh absorption feature of 2 209 nm and fe rich chlorite average wavelength of the feoh absorption feature of 2 249 nm in weakly altered rocks white mica compositions also vary with host lithology the aloh absorption feature occurs at longer wavelengths in white mica in dacite and andesite compared to adjacent rhyolitic rocks suggesting that higher fe and mg in the host lithology affects the composition of white mica two zones of intense hydrothermal alteration above the battle and hw orebodies have distinctive swir spectral characteristics with the aloh and feoh features occurring at shorter wavelengths 2 197 and 2 240 nm respectively small anomalous zones of alteration were also identified in the thelwood valley area where minor mineralized zones are present as broad zones of fine grained white mica sericite alteration are ubiquitous throughout the myra falls property alteration proximal to ore cannot be identified simply by visual logging of drill core alteration zonation may be determined by subtle shifts in white mica spectral characteristics this study indicates that swir analysis may be an effective field based exploration tool for quantifying the intensity of alteration associated with vhms orebodies and that trends in mineral compositions even in very fine grained rocks can be used as mine scale vectors to ore

lithogeochemical and stable isotopic insights into submarine genesis of pyrophyllite altered facies at the boco prospect western tasmania the boco prospect is a large fault dismembered pipelike hydrothermally altered zone in the mount read volcanics of western tasmania it is a synvolcanic alteration zone hosted by felsic volcanic rocks formed in a subaqueous proximal intracaldera setting previous detailed geochemical and geophysical surveys and extensive drill testing have indicated it contains no economic metals the strong to intense pervasively quartz phyllosilicate pyrite altered northern segment of the prospect is semiconcentrically zoned short wavelength infrared swir spectral analysis has revealed that phyllosilicate assemblages grade from phengitic white mica in the least altered peripheries through normal potassic white mica to central zones containing kaolinite slightly sodic white mica and pyrophyllite mass balance calculations indicate average net mass losses in the altered facies were about 10 to 30 g 100 g mainly owing to loss of sio2 which implies very high hydrothermal water rock ratios whole rock oxygen isotope compositions of the enclosing least altered felsic rocks 18o values 8 2 11 7 are indistinguishable from those of altered facies 9 6 11 8 we attribute the former to low temperature diagenetic isotopic exchange with 0 per mil 18o seawater in the peripheral least altered zones and the latter to exchange with 3 to 6 per mil 18o hydrothermal fluids at high water rock ratios and temperatures generally greater than 220 c and locally greater than 270 c in the intensely altered facies pyrite sulfur isotope compositions in the boco altered facies 34s values 1 2 7 2 are distinctly lower than most tasmanian massive sulfide deposits 6 15 compatible with a dominantly magmatic source of sulfur the alteration mineral assemblages estimated mass changes and isotopic data show that the boco alteration system was formed by a large volume of focused acidic hydrothermal fluid which had an oxygen isotope composition of 3 to 6 per mil 18o at and temperature greater than 270 c the slightly 18o enriched fluid isotope composition suggests derivation from either mixed magmatic fluid and seawater or isotopically evolved sea water its advanced argillic altered facies place boco among a newly recognized class of southeast australian cambrian volcanic hosted prospects and deposits these include chester basin lake western tharsis and north lyell in tasmania and rhyolite creek hill 800 and mike s bluff in eastern victoria swir spectral analyses with field portable spectrometers allow early discrimination of this type of hydrothermally altered system and can potentially assist subsequent exploration in mapping facies zonation

the great tonalite sill emplacement into a contractional shear zone and implications for late cretaceous to early eocene tectonics in southeastern alaska and british columbia the late cretaceous to early tertiary great tonalite sill of southeast alaska and british columbia is a very long 1 000 km and thin 25 km orogen parallel composite batholith which lies between the insular superter rane including the alexander and wrangellia terranes and the intermontane superterrane including the stikine and cache creek terranes the batholith is delineated by many steep sheet like plutons which are dominated by northwest southeast striking concordant fabrics with steep lineations that formed during deformation in a country rock shear zone prior to the complete crystallization of the magmas deformation in this shear zone is dominated by northeast southwest directed contraction orthogonal to the orogenic strike associated with a component of northeast over southwest high angle shear the steep multiple dike like nature of the body and its emplacement during orogenic contraction imply that ascent and emplacement have been achieved by dike wedging mechanisms along the deep reaching shear zone the remarkable narrowness of the great tonalite sill is probably the result of melting at the base of a very localized zone of thickened crust produced by the associated narrow contractional shear zone extending along the orogen length such a shear zone of late cretaceous to early tertiary age lying along 800 km of the possible boundary between the insular and intermontane superterranes implies that it may represent the actual boundary between them if this hypothesis is correct it implies that the large scale tectonic regime during emplacement of the great tonalite sill was predominantly orthogonal and not obliquely dextral as has been indicated from paleomagnetic data

geodynamics of the western part of the mongolia okhotsk collisional belt trans baikal region russia and mongolia abstract after the western edge of the mongolian microcontinent joined the siberian continent in the region of central mongolia in the earliest permian these two continental blocks remained turned at an angle of about 120 with respect to each other and separated on greater extent of their present day boundary by an enormous gulf of the paleopacific called the mongolia okhotsk ocean closure of this ocean at the early middle jurassic boundary led to the complete collision of siberia and mongolia which by then had already become part of the mongolia north china continent this main collisional episode which lasted through the middle and late jurassic involved thrusting folding and magmatism and produced the mongolia okhotsk belt the onon island arc which was located in the mongolia okhotsk ocean was squeezed between the two major continents inasmuch as the third element the island arc was involved in the collision it is reasonable to distinguish two branches of the mongolia okhotsk suture these branches control the spatial distribution of gold mineralization in the trans baikal region on the southeastern periphery of siberia the crust thickened considerably after the collision and a plateau like uplift formed in the early cretaceous when compression ceased the collisional uplift collapsed and the thrusts were transformed into low angle normal faults the motions on which were responsible for the formation of rift basins and exhumation of metamorphic core complexes

structural constraints on the evolution of the central asian orogenic belt in sw mongolia we provide a detailed description of the structures along a 300 km long and 50 km wide transect across the central asian orogenic belt caob in southwestern mongolia covering the precambrian dzabkhan continental domain with overthrust neoproterozoic ophiolites in the north lake zone a silurian devonian passive margin association gobi altai zone and oceanic domain trans altai zone in the center and a continental area south gobi zone in the south structural analysis suggests late cambrian collapse of the thickened lake zone continental crust leading to stretching of the lithosphere and followed by silurian devonian formation of oceanic crust in the trans altai domain subsequent emplacement of devonian carboniferous and late carboniferous magmatic arcs occurred on the gobi altai and south gobi zone crusts respectively during e w shortening finally the entire system was affected by n s convergence from the permian to jurassic leading to heterogeneous shortening of the orogenic domain the model best fitting these observations is one of generalized westward drift of the tuva mongol dzabkhan baydrag ribbon continents during the silurian devonian associated with westward subduction of the mongol okhotsk ocean and sequential growth of syn convergent magmatic arcs back arc basins opened during this period in the area of the western paleoasian ocean the present day shape of the caob in southern mongolia was probably formed during permian to mesozoic anticlockwise rotation and folding of the tuva mongol dzabkhan baydrag continental ribbons combined with a strike slip transpressional reactivation of ancient transform boundaries in the paleoasian oceanic domain all continental and oceanic crustal domains were reactivated and intensely deformed during this convergence in a style controlled by crustal rheology and a heterogeneous permian magmatic thermal input the sequence of tectonic events is tested against published paleomagnetic data paleogeographic reconstructions and tectonic models leading to a revised model for the accretion of juvenile crust to a continental margin in the caob of southern mongolia

high resolution hyperspectral based continuous mineralogical and total organic carbon analysis of the eagle ford group and associated formations in south texas hyperspectral sensing is used to generate mineral maps of a fine grained vertical eagle ford group cored section and underlying buda limestone and del rio formation in south texas this technology produces a map that shows the distribution of minerals on the core surface three different cameras within the hyperspectral core imaging system were used to image a 99 1 m 325 ft core a 1 line scan camera which produces a high resolution red green blue 120 m natural color photograph of the dry core from the visible light spectrum 2 short wave infrared swir spectrometer 300 500 m resolution and 3 long wave infrared lwir spectrometer 300 500 m resolution in 2016 the introduction of a new high resolution lwir spectrometer made it possible to identify minerals in cores that were not detected by previous swir systems high resolution hyperspectral imaging technology using both the swir and lwir spectra provides a significant step toward quantifying mineralogy and total organic carbon hyperspectral imaging is a powerful tool for studying textural and fabric relationships because it detects and highlights the major mineralogical changes that occur between depositional beds and among depositional features calcite compositional variations and cyclicity appear to be closely related the sr rich calcite appears to indicate a smaller allochem size dominance as well as the slower sedimentation rates that are required for nannofossils to settle from suspension finally the observed diagnostic cyclicity of the lower eagle ford can be related to coccolithophore productivity

hydrothermal alteration characteristics of the chating cu au deposit in xuancheng city anhui province china significance of sericite alteration for cu au exploration abstract the chating cu au deposit in xuancheng city anhui province is characterized by porphyry style mineralization with intensive hydrothermal alteration short wave infrared reflectance spectroscopy was used to systematically analyze the alteration of drill cores from two cross sections eleven alteration minerals sericite smectite kaolinite dickite chlorite epidote gypsum carbonate iron oxide saponite and prehnite were identified and the relative abundances of individual minerals at various depths were calculated by depth of absorption peak in these minerals iron oxides and gypsum are probably related to supergene process and other alteration minerals are hydrothermal alteration minerals the mineral assemblages and their spatial distributions indicate that the alteration patterns in this cu au deposit were controlled mainly by water rock interaction of the magmatic hydrothermal process resulting in a typical porphyry style hydrothermal mineralization system a saponite smectite k feldspar anhydrite gypsum alteration assemblage is located mainly in the host quartz diorite porphyry and is minor in the wall rocks of limestone and a post mineralization diorite porphyry a sericite chlorite alteration assemblage was widely developed in the quartz diorite porphyry and the intensity of alteration decreases gradually outward from the center to the margins of the deposit a kaolinite calcite alteration assemblage is mainly located on the top of the quartz diorite porphyry and in the surrounding limestone the physiochemical conditions of the hydrothermal fluid such as temperature and ph control the compositional variations of specific alteration minerals the most remarkable feature is a subtle change in octahedral al cation content of sericite as identified by the change in wavelength of sericite al oh absorption peak position muscovite is the main component of sericite with a trace amount of phengite the cu au grades are negatively correlated with the wavelength of sericite al oh absorption peak position because high ore grades are associated with relatively shorter al oh wavelengths corresponding to a high al si ratio in sericite i e towards muscovite this correlation suggests that the ore metal tends to be enriched and precipitated in an acidic environment of the alteration system in addition a lateral variation across the deposit in al oh wavelength indicates that the acidity of the hydrothermal fluids decreases gradually from the center of the deposit outward to the wall rocks whereas the variation of sericite al oh wavelength with depth suggests an increase in fluid ph with decreasing depth the alteration patterns imply that during mineralization the ore forming fluids probably migrated from the southwest in the deep part of the porphyry system towards the northeast near the surface based on the spectral alteration mapping it is concluded that there were at least three stages of hydrothermal activity in the chating mining district an early potassic skarn hydrothermal alteration stage an intermediate propylitic sericite medium low temperature alteration stage and a late kaolinite dickite epithermal stage the sericite alteration stage is temporally related to cu au mineralization leading to the formation of the main orebody at chating as the current exploration is still focused in the sericite alteration zone it is inferred that deep exploration has great potential in the chating district

evolution of the solonker suture zone constraints from zircon u pb ages hf isotopic ratios and whole rock nd sr isotope compositions of subduction and collision related magmas and forearc sediments abstract the solonker zone in northern inner mongolia china is considered as the suture between the north china craton and the south mongolian microcontinent two magmatic belts are recognized along the suture zone a subduction related magmatic belt represented by the baolidao arc rocks and a younger collision related granite belt represented by the halatu granites we use zircon u pb ages zircon in situ hf isotopic analyses and whole rock nd sr isotopic data of the two magmatic belts and related forearc sediments the xilinhot metamorphic complex to constrain timing of the suturing and to discuss the petrogenesis of the magmatic rocks a gabbroic diorite bld 1 of the baolidao arc was dated at 310 5 ma by shrimp this sample shows an e nd t value of 2 5 and i sr of 0 7052 hf isotopic analyses on 25 zircons from the same sample show e hf t 5 4 to 11 5 another diorite sample xh 2 of the same arc from south of xilinhot displays even more depleted isotopic compositions with e nd t 5 6 and i sr 0 7037 the main population of zircons from this sample have highly variable and depleted hf isotopic compositions e hf t 0 18 3 the large variation in hf isotopic composition of zircons with largely the same crystallization age from a single pluton is explained by a mixing process between depleted mantle derived magma and continental crust in an active continental arc setting the halatu granite hlt 2 was dated at 234 7 ma by shrimp zircons from the granite also show a large variation of e hf t values 9 1 to 26 despite most samples having whole rock e hf t 2 the large variation in e hf t values suggests that the granite formed probably by partial melting of two source regions a dominant juvenile crust and a subordinate old continental crust most zircons from the xilinhot metamorphic complex show ages comparable with those of the baolidao arc rocks suggesting that the protolith of the metamorphic complex was probably deposited during or after arc magmatism some zircons however show precambrian ages that fall into two groups one with ages of 780 900 ma resembling those from the south mongolian microcontinent and the other with ages of 1524 2900 ma similar to those of the north china craton thus the protolith of the metamorphic complex probably formed in a forearc basin during convergence of the two continents and metamorphosed subsequently during collision in the late paleozoic our zircon age data thus constrain timing of collision between the south mongolian microcontinent and the north china craton to have been between 296 and 234 ma

alteration mapping with short wavelength infrared swir spectroscopy on xiaokelehe porphyry cu mo deposit in the great xing an range ne china metallogenic and exploration implications abstract the newly discovered xiaokelehe porphyry cu mo deposit pcd is situated in northern part of the great xing an metallogenic belt northeastern china the syn mineralization granodiorite porphyry was intruded by multiple phases of post ore barren monzonite diorite porphyry and granite porphyry leading to complex and overprinting hydrothermal alteration patterns this paper present new data on the alteration mineralogy vein paragenesis sulfide assemblages and swir short wavelength infrared spectroscopy at xiaokelehe and discuss how swir spectral data can help to understand hydrothermal fluid evolution and assist pcd exploration at xiaokelehe oligoclase epidote alteration is distributed at the deeper levels of the granodiorite porphyry but played little role in mineralization the following potassic alteration hydrothermal biotite and k feldspar was developed in the granodiorite porphyry with the main cu mo mineralization drill core logging suggests that the subsequent chlorite illite alteration affected almost the entire granodiorite porphyry and is spatially and genetically associated with minor cu mineralization the youngest quartz muscovite pyrite alteration dominated in the upper level and outer parts of the pcd and overprints the earlier alteration phases with only very minor mineralization the short wavelength infrared swir analysis results indicate that chlorite and white micas illite and muscovite are the most abundant alteration minerals at xiaokelehe the wavelengths of fe oh band pos2250 of chlorite show a decreasing trend away from the granodiorite porphyry into the surrounding sedimentary wall rocks probably reflecting a drop in temperature and fe contents of the hydrothermal fluids the illite crystallinity ic values of white micas show a reverse trend different from many pcds which is likely caused by the distribution pattern of illite and muscovite formed in the ore proximal chlorite illite and ore distal quartz muscovite pyrite alteration respectively at xiaokelehe cu and mo mineralization is mainly distributed in quartz veins or disseminated within the potassic alteration zones resembling typical pcds meanwhile chlorite illite alteration is also associated with minor cu mineralization thus areas with intensive chlorite illite alteration overlapping on potassic alteration likely represent the best exploration targets for high grade cu mo mineralization these target areas coincide spatially with areas of lower ic 2245 nm values suggesting the latter two are effective vectoring tools for pcd exploration at xiaokelehe

biotite chemistry and the role of halogens in archaean greenstone hosted gold deposits a case study from geita gold mine tanzania abstract geita hill is one of the largest tanzanian gold deposits located southwest of lake victoria and 2 km along strike from the giant nyankanga deposit the deposit is hosted by metasedimentary rocks dominated by ironstones and intruded by numerous diorite dykes textural structural and geochronological observations indicate that the gold mineralisation overprints all the ductile fabrics and the late orogenic d6 reverse faulting event suggesting that gold was introduced during later d7 and d8 events the metamorphic background is characterized by biotite k feldspar actinolite pyrhotite which is overprinted by the gold related alteration consisting of sulfidation fronts veins and micro fractures dominated by quartz biotite k feldpar pyrite the almost identical mineralogy of the mineralised assemblage and the metamorphic background makes it difficult to identify the source the effect and the spatial extent of the mineralising fluid as part of this study detailed analyses of biotite were conducted in order to identify the nature of the mineralising fluid and its spatial effect across the geita hill deposit results show that the mineralised assemblage is slightly more oxidized pyrite magnetite compared to the metamorphic background pyrrhotite magnetite the intense sulfidation within the ore zone resulted in the formation of mg rich biotite which grades into more fe rich biotite away from the ore zone this change in biotite chemistry causes a shift in the swir fe oh 2250 nm absorption feature to lower wavelengths which is also correlated with an increase in gold grade within the mineralised zone the abundance of f in biotite significantly increases within the ore zone indicating the presence of f rich hydrothermal fluids during mineralisation late timing of mineralisation synchronous with the emplacement of voluminous high k granites and the presence of k and f bearing fluids indicate a genetic connection between the mineralising fluids and the late granites biotite grains from different deposits types porphyry iocg lode au appear to have distinct composition suggesting that the source of the fluids involved in the formation of each deposit type has a characteristic halogen chemistry

lithosphere rheology and active tectonics in mongolia relations between earthquake source parameters gravity and gps measurements in this paper we use observations of earthquake source parameters and gravity to investigate the mechanical properties and the active faulting of the lithosphere in mongolia well determined earthquake centroid depths including 10 from inversions of p and sh waveforms that are presented here for the first time show that the seismogenic thickness ts within mongolia itself is less than 20 km however to both the east in parts of the lake baikal rift system and the west adjacent to the junggar basin and kazakhstan platform the seismogenic thickness is considerably greater and includes essentially the whole crust from the admittance between the free air gravity and the topography and also from profiles across a flexural foreland basin we determine the effective elastic thickness te in central mongolia to be 30 km in both mongolia and its surroundings te is comparable with ts and where it is well determined te ts these data are consistent with the view that the strength of the continental lithosphere resides in its seismogenic part which in mongolia is the upper crust but to both the east and west appears to be the whole crust the earthquake source parameters also allow us to ask how the active faulting in mongolia accommodates the velocity field revealed by gps measurements it is likely that the entire mongolian altay range in the west rotates counter clockwise relative to stable asia and is responsible for the distributed e w left lateral shear seen further east in central mongolia the admittance observations show no evidence at the present day for convective mantle support or a hotspot responsible for the elevated region of the hangay dome in central mongolia even though the geochemical data from nodules in late cenozoic basalts and seismic tomography studies suggest elevated temperatures at shallow depths 125 km and probably thinned lithosphere

hydrothermal alteration and short wavelength infrared swir characteristics of the tongshankou porphyry skarn cu mo deposit yangtze craton eastern china abstract the early cretaceous tongshankou cu mo deposit is located in the eastern yangtze craton and comprises both porphyry and skarn mineralization the porphyry ore is hosted in a granodiorite porphyry with the skarn mineralization found along the contacts with the carbonate host rocks alteration in the porphyry mineralization can be divided into three stages potassic alteration phyllic alteration and a carbonate stage with phyllic alteration associated with the main porphyry mineralization no propylitic alteration is present at tongshankou the skarn type alteration comprises five stages early skarn stage late skarn stage oxide stage quartz sulfide stage and late vein stage short wave length infrared swir analysis identified 15 hydrothermal minerals in the tongshankou deposit including illite dickite halloysite phengite talc muscovite saponite gypsum chlorite prehnite montmorillonite serpentine phlogopite actinolite kaolinite with montmorillonite illite and chlorite being the most common swir parameters and the electron microprobe results of chlorites show that chlorites close to the mineralization center tend to be iron rich and have high feoh absorption position pos 2250 2251 nm consequently chlorite may be a useful indicator mineral for mineralization in the tongshankou deposit pos 2250 is not correlated to temperature as calculated using a chlorite geothermometer but does correlate with the iron contents of the chlorites our results show that the ore forming fluids are fe rich in the proximity to the mineralization but mg rich towards the distal area unlike in other porphyry deposits the white mica show no consistent variation in the tongshankou deposit and cannot be used as vectors towards mineralization the fe mg al poor carbonate host rocks of the tongshankou deposit restrict the development of a propylitic alteration zone the fe mg al host rocks also prevent tschermak exchange in white mica siiv mg fe vi alivalvi making white mica pos 2200 and illite crystallinity ic randomly distributed our results show that swir spectroscopy of chlorite may be an applicable exploration tool in skarn related hydrothermal systems

precambrian crystalline basement in southern mongolia as revealed by shrimp zircon dating single zircon ages determined by ion microprobe shrimp ii for granitoid gneisses from the southern slope of the baga bogd massif gobi altai southern mongolia reveal several episodes of zircon growth ranging from late palaeoproterozoic to late cambrian the oldest events are documented by a zircon crystallization age for a gneiss protolith at 1519 11 ma and by a xenocrystic zircon from a dark grey augen gneiss yielding an age of c 1701 ma discrete igneous events are recorded in granite gneisses with protolith emplacement ages of 983 6 956 3 and 954 8 ma these ages provide the first record of early neoproterozoic magmatic activity in this region a much younger and discrete magmatic event is recorded by several dioritic to granitic orthogneisses which are tectonically interlayered with the older gneisses and have protolith emplacement ages between 502 and 498 ma these late cambrian granitoids of calc alkaline affinity are likely to have been emplaced along an active continental margin and suggest that the baga bogd precambrian crustal fragment was either docked against the southward present day coordinates growing margin of the caob or was a large enough crustal entity to develop an arc along its margin we speculate that the precambrian gneisses of this massif may be part of a crustal fragment rifted off the tarim craton

a new paleogeographic configuration of the eurasian landmass resolves a paleomagnetic paradox of the tarim basin china 1 new paleomagnetic data from permian red beds and middle jurassic limestones from the tarim basin pose a paradox their declinations are similar to upper carboniferous to neogene rocks collected from the same sections and their inclinations parallel present values when assuming that lower than expected inclinations in continental sedimentary rocks arise from inclination shallowing effects then the paleolatitudes of all upper carboniferous to present rocks from tarim are indistinguishable local vertical axis block rotations occurring in the last 20 million years explain why declinations vary at different localities in the basin our middle jurassic data positions tarim 23 6 8 4 farther south than that predicted from the coeval reference pole for eurasia however no geologic argument exists to support the closure of a large ocean basin between tarim and siberia since the middle jurassic thus the paradox are the rocks from tarim totally overprinted or is the middle mesozoic part of the reference eurasian apparent polar wander path erroneous several lines of evidence suggest the tarim rocks are not remagnetized we conclude that tarim has experienced little or no apparent polar wander since the carboniferous moreover our middle mesozoic reconstruction of eurasia using the new middle jurassic pole from tarim results in a more geologically compatible solution for the eastern asian blocks over previous reconstructions

shortwave infrared spectral analysis of hydrothermal alteration associated with the pebble porphyry copper gold molybdenum deposit iliamna alaska the pebble cu au mo porphyry deposit is located approximately 320 km southwest of anchorage alaska shortwave infrared swir spectroscopy on drill core from the deposit has been used to document the distribution of alteration assemblages characterized by subtle variations in phyllosilicate minerals that cannot be confidently distinguished by visual criteria alone at pebble these phyllosilicate alteration types have different histories of metal introduction and or redistribution delineation of the distribution of these assemblages is critical to the geologic and genetic interpretations of the deposit spectral absorption features between 1 300 and 2 500 nm in particular small shifts in the position of the absorption wavelength related to aloh bonds around 2 200 nm allows distinction among illite sericite kaolinite and pyrophyllite bearing alteration assemblages electron microprobe and x ray diffraction analyses were used to validate the chemical composition and crystallinity of the phyllosilicate minerals identified using spectral data the results confirm the use of swir spectroscopy to confidently identify and spatially delineate phyllosilicate alteration assemblages at pebble these alteration types include potassic illite kaolinite quartz illite pyrite sericite pyrophyllite quartz sericite pyrite and sodic potassic assemblages the highest gold and copper concentrations within the deposit are in the eastern pluton and are coincident with low aloh values associated with pyrophyllite and sericite alteration an additional zone of low aloh values not associated with high metal grades occurs in the northeast along the margins of the deposit coincident with quartz sericite pyrite alteration the approach described here has significantly improved three dimensional alteration mapping and shows that short wave infrared spectroscopy may successfully distinguish variations in phyllosiclicate species this has implications for exploration because clay speciation is genetically related to the distribution of metals in the pebble deposit the recognition and utilization of these relationships has produced a robust three dimensional alteration model which can be applied to optimizing mine planning comminution and mineral process design

hypogene and supergene alteration of the late palaeozoic ratburi limestone during the mesozoic and cenozoic thailand surat thani province implications for the concentration of mineral commodities and hydrocarbons an interdisciplinary study of the upper carboniferous to middle permian ratburi group peninsular thailand is presented the investigation involved sedimentary petrography inorganic geochemistry sr c o isotope analyses micropalaeontology as well as radio carbon age dating emphasis was placed on the post depositional evolution of the ratburi limestone in the surat thani province the holocene chemical residues and the various calcite and dolomite minerals which have formed since the late palaeozoic in the ratburi limestone are the product of a complex multistage alteration which is called supergene and hypogene karstifications respectively sedimentation took place in a shelf environment with some reefs evolving during the late murgabian at the shelf margin there was no pre concentration of elements except for ca and f during sedimentation diagenetic neomorphism and cementation under marine and freshwater conditions caused the ratburi limestone to convert into a marble like rock fabric selective dolomitization is of local scale and has impacted only on part of the ratburi limestone during the lower to upper permian a significant enhancement of pore space and better conduits were generated during the late cretaceous epithermal alteration the most favorable conditions for the accumulation of metals were provided during the high temperature stage of epithermal alteration when a low metal concentration with as zn sb u co and pb existed unlike the other elements sb was subject to a multiphase concentration giving rise to a considerable sb deposit in the region the most recent stage of karstification produced numerous caves dripstones tufa terraces and encrustations around brine pools in the study area this alteration originated from per descensum and per ascensum processes which may be traced back to 15 000 years before present the alteration of the ratburi limestone may be subdivided into two parts the prograde post depositional alteration beginning with diagenesis reached its temperature climax during epithermal subsurface alteration i the retrograde branch of alteration lasted until the most recent times the initial stages deposition and diagenesis took place under more or less closed system conditions relative to the succeeding stages of the prograde alteration which saw the strongest influx of metal bearing brine during the epithermal stage i the retrograde branch of alteration is element conservative

mapping advanced argillic alteration at cuprite nevada using imaging spectroscopy mineral maps based on airborne visible infrared imaging spectrometer aviris data were used to study late miocene advanced argillic alteration at cuprite nevada distributions of fe bearing minerals clays micas sulfates and carbonates were mapped using the tetracorder spectral shape matching system the al content of white micas increases toward altered areas and near intrusive rocks alunite composition varies from pure k to intimate mixtures of na k endmembers with subpixel occurrences of huangite the ca analogue of alunite intimately mixed na k alunite marks areas of relatively lower alteration temperature whereas co occurring na alunite and dickite may delineate relict hydrothermal conduits the presence of dickite halloysite and well ordered kaolinite but absence of disordered kaolinite is consistent with acidic conditions during hydrothermal alteration partial lichen cover on opal spectrally mimics chalcedony limiting its detection to lichen free areas pods of buddingtonite are remnants of initial quartz adularia smectite alteration thus spectral maps provide a synoptic view of the surface mineralogy and define a previously unrecognized early steam heated hydrothermal event faulting and episodes of hydrothermal alteration at cuprite were intimately linked to upper plate movements above the silver peak lone mountain detachment and growth collapse and resurgence of the nearby stonewall mountain volcanic complex between 8 and 5 ma isotopic dating indicates that hydrothermal activity started at least by 7 61 ma and ended by about 6 2 ma spectral and stable isotope data suggest that cuprite is a late miocene low sulfidation adularia sericite type hot spring deposit overprinted by late stage steam heated advanced argillic alteration formed along the margin of the stonewall mountain caldera

textural and chemical characteristics of diagenetic and hydrothermal alteration in glassy volcanic rocks examples from the mount read volcanics tasmania the mount black and sterling valley volcanics comprise a complex cambrian succession of originally glassy felsic to mafic submarine volcanic facies in western tasmania the mount black and sterling valley volcanics have been modified by the combined effects of diagenesis hydrothermal alteration and regional metamorphism metamorphosed diagenetic and hydrothermal alteration facies have been distinguished using a combination of alteration mineralogy overprinting relationships texture distribution intensity and whole rock geochemistry alteration facies that are interpreted to be the regionally metamorphosed equivalents of diagenetic clays and zeolites are regionally extensive and overprinted by the regional cleavage although widespread their distribution is patchy and their intensities are highly variable reflecting the complexity of the original textures in glassy volcanic rocks thin films of sericite carbonate and chlorite sericite hematite replace clays that coated original glassy surfaces at the onset of diagenesis prior to compaction feldspar quartz sericite chlorite sericite and chlorite sericite hematite alteration facies replace zeolites and clays that filled pore space and altered glass prior to and synchronous with compaction the final diagenetic alteration facies chlorite epidote began after compaction and continued during metamorphism diagenetic alteration involved significant mineralogical and textural changes but only minor changes in chemistry the chemical changes associated with diagenetic alteration facies are consistent with the interaction of rhyolitic and basaltic glass with seawater during burial alteration facies that are interpreted to be hydrothermal are local in distribution crosscut stratigraphic boundaries and involve significant changes in texture mineralogy and composition early hydrothermal alteration facies quartz sericite and calcite quartz hematite predated compaction and were synchronous with diagenesis chlorite calcite magnetite and chlorite pyrite alteration facies were synchronous with regional deformation and are associated with tectonic breccias faults and shear zones chlorite quartz calcite alteration facies postdated regional deformation