structural features and the evolutionary mechanisms of the basal shear zone of a rockslide abstract rockslides commonly form a shear zone to accommodate their displacements as such the landslide history and mechanism must be recorded in the structural features of the shear zone we investigated the basal shear zone of a 60 m thick rockslide body with a lateral displacement of 200 m on a dip slope and found the evolutionary mechanisms of a basal shear zone of a rockslide a basal shear zone on a dip slope is initiated along a lithologic boundary that is characterized by a high competency contrast such as pelitic rock and greenstone or chert and develops in the weaker rock which was pelitic rock in the present study the basal shear zone first develops with fracture of the rock mass followed by intragranular fracturing of rock fragments shear strain by landslide gradually localizes to a narrow zone in the fractured zone to form a clayey layer by cataclasis of rock fragments the rock fragments in the clayey layer become rounded by attrition and the clayey layer finally obtains shear surfaces with slickensides

geochemical compositions of ore related pyrite quartz and fluid inclusions of bangbu gold deposit in the indus yurlung zangbo suture zone tibet abstract the bangbu gold deposit is the largest au deposit and the only deposit in production within an orogenic au belt hosted by the indus yurlung zangbo suture zone in tibet strontium isotopes and in situ trace element data from ore related pyrite quartz and fluid inclusions were used to determine the composition of ore forming fluids the sources of ore components and ore forming processes arsenic se and ge are incorporated into au bearing pyrite by isomorphic substitution for s while co and ni replace fe in the pyrite lattice and au occurs either as lattice bound or in the form of nanoparticles in pyrite the individual fluid inclusions have au contents of 0 59 4 41 ppm with an average of 1 43 ppm single fluid inclusion analyses show a negative correlation between au and cl contents indicating that au did not complex with cl ions and was probably transported as au hs 2 aluminum is positively correlated with li and ge in ore related quartz consistent with a contribution from magmatic hydrothermal fluids the average 87sr 86sr ratio of fluid inclusions in quartz is 0 71577 which indicates a contribution from mantle derived material gold is likely to have been sourced from fluids evolved from mantle derived magma rather than the surrounding rocks

methane derived hydrocarbons produced under upper mantle conditions there is widespread evidence that petroleum originates from biological processes 1 3 whether hydrocarbons can also be produced from abiogenic precursor molecules under the high pressure high tem

tracing the transition of gold from source to sponge to sink the late timing of gold is a characteristic feature of orogenic gold deposits for many of these deposits gold and other metals were liberated from the host greenstone belt and or early sulfides concomitant with the syndeformational and fluid assisted metamorphic transition of pyrite to pyrrhotite and remobilized into late high grade ore shoots however this metamorphic driven gold upgrading model is usually inferred at least in part from mineral textures which can be equivocal in the absence of geochemical and or isotopic constraints herein we report new bulk mineral separate and in situ pb isotope results for minerals in key textures in the paleoproterozoic meliadine gold district arsenopyrite and pyrite porphyroblasts occur in paleoproterozoic quartz ankerite veins and are enveloped by remobilized pyrrhotite chalcopyrite and galena crystals that accompany gold in late microtextural sites a texture that forms the basis for the gold upgrading model early sieve textured arsenopyrite and pyrite are gold rich and tend to yield the least radiogenic pb isotope compositions high 207 pb 206 pb and 208 pb 206 pb ratios suggesting these relict domains escaped complete recrystallization during later reworking late inclusion free arsenopyrite and pyrite overgrowths scatter to more radiogenic pb isotope compositions low 207 pb 206 pb and 208 pb 206 pb ratios and are typically gold poor which we attribute to reworking and precipitation from a younger and more radiogenic fluid prior to and or during the precipitation of free gold in variably plunging high grade ore shoots at 1 90 to 1 85 ga remobilized sulfides are the youngest sulfide phases but locally yield low 206 pb 204 pb and 207 pb 204 pb ratios and thus spurious old model ages which overlap with the least radiogenic sieve textured arsenopyrite pyrite domains the isotopic signature of these remobilized sulfides was likely inherited from pb liberated during reworking of early arsenopyrite and pyrite and a second crustal pb source that was introduced during late remobilization our results highlight the importance of element recycling from early sulfides and or the neoarchean deposit host rocks during significantly younger paleoproterozoic reworking and gold remobilization the in situ pb isotope results of early and remobilized sulfides document the transition of gold from source to sponge to sink which is likely a feature that occurred during the formation of other orogenic style gold deposits

local and regional mass transfer during thrusting veining and boudinage in the genesis of the giant shale hosted paracatu gold deposit minas gerais brazil multiscale structural and geochemical studies have been applied to understand the genesis of the paracatu deposit in brazil a shallow dipping bulk tonnage vein style low grade au ag pb zn orebody hosted in 1000 ma black phyllites of the paracatu formation associated with intense shearing accompanying thrusting during the 680 ma brasiliano orogeny massive to laminated quartz sulfide carbonate veins and associated alteration and au mineralization formed early in the deformation history and these veins were boudinaged during subsequent progressive increase in shear strain geochemical profiles across the ore allow recognition of a relatively homogeneous protolith at 100 m scales with respect to ti al zr v and rare earth elements including a footwall with protolith attributes similar to those of the ore oxygen hydrogen and sulfur isotopes do not reveal a distinctive external fluid source rather they reflect fluid rock equilibration with the host phyllites during greenschist facies regional metamorphism detailed geochemical sampling around a prominent population of smaller boudinaged veins shows that si ca and sr were removed and al k and ti were residually concentrated during formation of synboudinage dark selvages this process of mass transfer occurred at scales more local than the processes responsible for ore genesis despite the local processes of chemical equilibration and redistribution many of the main ore components appear externally derived at scales broader than the orebody gold as ag sb bi and to some extent pb and zn show a strong spatial and statistical correlation with boudinaged quartz sulfide carbonate veins and these are surrounded by a broader 10 50 m vertical scale halo of enriched k ba and volatiles loss on ignition with depleted na and sr the majority of gold is present as inclusions in pyrite and arsenopyrite within and immediately surrounding the veins and gold bearing pyrite shows mineral chemistry consistent with a hydrothermal origin the main population of large veins locally preserve preboudinage complex internal vein textures including sulfide rich wall rock laminae similar to laminated fault fill veins in many orogenic style vein deposits these larger veins contain most of the gold in the paracatu resource metals were most likely sourced distal to the paracatu formation and were precipitated in sheeted shear or tensile veins during the early stages of the brasiliano thrusting the oblate strain recorded by the boudinaged mineralized veins is anomalous and distinctive to paracatu at km scales even though the thrusting is regional although the orebody may have been physically dislocated by thrusting from the place where the early veins formed the anomalous strains recorded suggest a perturbation in the footwall to the regional thrust or perhaps a spatially restricted competency contrast within the stratigraphy which contributed to the localization of the present mineralization during the thrusting

on the feasibility of inversion of single well microseismic data for full moment tensor the existing paradigm widely accepted in the microseismic community asserts the impossibility of unambiguous estimation of full seismic moment tensor from three component data recorded in a single straight borehole the statement of inversion nonuniqueness related to the lack of illumination of the off plane moment component in the zero solid angle ray apertures tacitly assumes the slowness vectors normal to the relevant wave fronts to be confined to the plane containing the ray trajectories although such arrangements of the rays and slownesses do take place for vertical wells drilled in horizontally layered isotropic and vti transversely isotropic with a vertical symmetry axis formations azimuthal anisotropy commonly expected for hydraulically fractured hydrocarbon bearing shales makes the slowness vectors deviate from a plane arrange themselves into nonzero solid angle apertures and yield theoretically unique inverse problems for seismic moment tensors this paper examines those problems for the anisotropy parameters characterizing fractured shales and siltstones in the bakken their strong azimuthal anisotropy entails not only formally unique but importantly for practical applications well posed inverse problems resulting in robust estimates of the complete moment tensors from single borehole data

serpentinization carbon and deep life the aqueous alteration of ultramafic rocks through serpentinization liberates mantle carbon and reducing power serpentinization occurs in numerous settings on present day earth including subduction zones mid ocean ridges and ophiolites and has extended far into earth s history potentially contributing to the origins and early evolution of life serpentinization can provide the energy and raw materials to support chemosynthetic microbial communities that may penetrate deep into earth s subsurface microorganisms may also influence the composition and quantity of carbon bearing compounds in the deep subsurface however conditions created by serpentinization challenge the known limits of microbial physiology in terms of extreme ph access to electron acceptors and availability of nutrients furthermore the downward transport of surface carbon and subsequent mixing with calcium rich fluids at high ph contributes to the precipitation and immobilization of carbonate minerals the following chapter will explore the physiological challenges presented by the serpentinite environment data from studies of serpentinite hosted microbial ecosystems and areas in need of further investigation physical and chemical consequences of serpentinization serpentinization is an alteration process of low silica ultramafic rocks characteristic of the lower oceanic crust and upper mantle these rocks are rich in the minerals olivine and pyroxene water rock reactions result in the oxidation of ferrous iron from olivine and pyroxene resulting in the precipitation of ferric iron in magnetite fe3o4 and other minerals and in the release of diatomic hydrogen h2 at low temperatures 150 c the reaction results in extremely high ph commonly above 10 the combination of h2 and co2 or co under highly reducing conditions leads to formation of methane and other hydrocarbons through fischer tropsch type ftt synthesis mccollom and seewald 2001 charlou et al 2002 proskurowski et al 2008 mccollom 2013 serpentinization also results in volume changes in the altered materials making serpentinites less dense than

stable c o and s isotope record of magmatic hydrothermal interactions between the faleme fe skarn and the loulo au systems in western mali the gara yalea and gounkoto au deposits of the 17 moz loulo mining district largely hosted by the kofi series metasediments are located several kilometers to the east of the 650 mt fe skarn deposits in the adjacent faleme batholith the au deposits are interpreted to have formed through phase separation of an aqueous carbonic fluid which locally mixed with a hypersaline brine of metaevaporite origin recognition of an intrusive relationship between the faleme batholith and kofi series opens the possibility that the fe skarns and au deposits are part of the same mineral system in this paper we combine new 13c 18o and 34s data from the karakaene ndi skarn au occurrences along the western margin of the kofi series and zircons within plutonic rocks of the faleme batholith we combine these with existing data from the loulo au deposits to model the contribution of magmatic volatiles to au mineralization c and o isotope compositions of auriferous carbonate quartz sulfide veins from the loulo au deposits have wide ranges 13c 21 7 to 4 5 and 18o 11 8 to 23 2 whereas values from carbonate veins in kofi series au prospects close to the faleme batholith and the karakaene ndi fe skarn deposit have more restricted ranges 13c 16 8 to 3 7 18o 11 4 to 17 2 and 13c 3 0 1 18o 12 6 1 respectively kofi series dolostones have generally higher isotopic values 13c 3 1 to 1 3 and 18o 19 1 to 23 3 pyrite from kofi series au prospects adjacent to the faleme batholith have a wide range of 34s values 4 6 to 14 2 similar to pyrite from the karakaene ndi skarn 2 8 to 11 9 whereas 34s values of pyrite and arsenopyrite from the loulo deposits are consistently 6 comparison of the c and o isotope data with water rock reaction models indicates the loulo au deposits formed primarily through unmixing of an aqueous carbonic fluid derived from the devolatilization of sedimentary rocks with an organic carbon component isotopic data are permissive of the hypersaline brine that enhanced this phase separation including components derived from both kofi series evaporite horizons interlayered with the dolostones and a magmatic hydrothermal brine this magmatic hydrothermal component is particularly apparent in o c and s isotope data from the gara deposit and au prospects immediately adjacent to the faleme batholith

multistage sedimentary and metamorphic origin of pyrite and gold in the giant sukhoi log deposit lena gold province russia gold mineralization at sukhoi log in eastern siberia is hosted in a deformed neoproterozoic organic bearing and pyritic black shale and siltstone sequence that is folded into a tight overturned anticline the deposit contains about 30 million ounces of gold at an average grade of 2 0 g t au and is one of the largest known undeveloped gold resources the high grade gold zone forms a gently dipping tabular body in the core of the anticline the best gold grades occur in narrow bedding parallel pyrite quartz veinlets that have been folded during the main deformation event lower grade gold is associated with disseminated pyrite developed in and around the high grade core of the deposit detailed paragenetic studies of the mineralization and host rocks have defined six stages of pyrite development in the carbonaceous sediments the two earliest forms of pyrite termed py1 and py2 are commonly developed in stratiform layers of micron sized crystals framboids and fine euhedra which are interpreted as synsedimentary to early diagenetic in origin coarser grained bedding parallel aggregates of inclusion rich pyrite termed py3 contain inclusions of arsenopyrite native gold and gold tellurides and are interpreted to form during late diagenesis and earliest deformation coarse euhedral pyrite py4 overgrows the earlier pyrite py1 py2 and py3 and the slaty cleavage developed in the host rocks indicating a syndeformation timing late stage inclusion free pyrite py5 overgrows and replaces earlier sulfides and is considered to be syn to late deformation laser ablation inductively coupled plasma mass spectrometry la icpms analyses of the various pyrite types indicate that the synsedimentary py1 contains the highest levels of invisible gold varying from 0 4 to 12 1 ppm with a mean of 3 22 ppm au and 1 900 ppm as py1 is also enriched in a suite of trace elements mo sb ni co se te ag cu pb zn mn ba cr u v which are similar to those concentrated by organic processes in euxinic sedimentary environments later generations of pyrite from py2 to py5 including pyrite in bedding parallel pyrite quartz veinlets contain progressively lower contents of invisible gold and most other trace elements however this metamorphic and postmetamorphic pyrite contains microinclusions of free gold arsenopyrite pyrrhotite sphalerite and chalcopyrite the paragenetic textural and chemical relationships at sukhoi log suggest that gold was clearly initially introduced prior to cleavage development accompanying sedimentation of the organic rich shales and fixed during diagenesis within the structure of diagenetic arsenian pyrite subsequently accompanying deformation gold was liberated from recrystallized diagenetic pyrite to become concentrated as free gold and gold tellurides within metamorphic pyrite and folded bedding parallel pyrite quartz veinlets two key processes are considered vital to the formation of the sukhoi log deposit original synsedimentary and early diagenetic concentration of gold dissolved within arsenian pyrite in organic rich black shales and metamorphic processes that liberated gold from the early forms of arsenian pyrite to be concentrated as free gold and gold tellurides within late diagenetic and metamorphic pyrite and associated pyrite quartz veinlets in the core of an overturned anticline these ore forming processes are unlikely to be unique to sukhoi log other black shale and turbidite hosted deposits that occur in rifted continental margin environments which have undergone collision and basin inversion may form by similar processes

bicarbonate rich fluid inclusions and hydrogen diffusion in quartz from the libcice orogenic gold deposit bohemian massif abstract unusual paleofluid composition is reported for the libcice orogenic type gold deposit located in the central bohemian plutonic complex cbpc czech republic unexpected bicarbonate rich fluids and their complex chemistry variations characterize primary fluid inclusions from the main gold bearing quartz vein a detailed microthermometry laser raman micro spectroscopy lrms and sem cathodoluminescence study was used to understand the complex chemistry and p t x history the results indicate the presence of h 2 o and h 2 o co 2 ch 4 n 2 h 2 s fluids the latter displaying variations of the co 2 ch 4 ratio in the gaseous phase from 6 8 to 0 06 variation of the ch 4 content across single grains and between different levels of the mine was recorded the presence of nahcolite h 2 up to 6 mol and ethane 0 0 2 mol in the fluids were also discovered by lrms potential models for the formation of different types of fluids present in the deposit are discussed including the genesis of hco 3 rich fluids as well as h 2 and c 2 h 6 presence in the primary fluid inclusions the potential influence of organic matter bearing sediments as well as the impact of the intrusion of cbpc re equilibration and or re speciation of fluid inclusions during the post entrapment history is considered to have the main impact on the complex paleofluid chemistry based on the thermodynamic modeling h 2 diffusion into the fluid inclusions was shown to be the main reason for the ch 4 variation on the scale of a single grain as well as across the whole vein although the exact processes of production formation of hco 3 and h 2 at the libcice deposit remain open to discussion reactions in the c o h system are considered to be a possible formation mechanism this work also contributes to our understanding of the importance of post entrapment modifications and reactions in the c o h system on interpretation deciphering the processes in orogenic type deposits

metal source and fluid rock interaction in the archean bif hosted lamego gold mineralization microthermometric and la icp ms analyses of fluid inclusions in quartz veins rio das velhas greenstone belt brazil the lamego orogenic gold deposit 440 742 oz gold measured reserves and 2 4 million t measured resources with an average grade of 5 71 g t au and a cut off grade of 2 15 g t au anglogold ashanti corrego do sitio mineracao s a aga personal communication 2014 is located in the 5 km long trend that includes the world class cuiaba deposit it is hosted in the neoarchean metavolcano sedimentary rocks of the rio das velhas greenstone belt quadrilatero ferrifero brazil mineralization is associated mainly with metachert banded iron formation bif and carbonaceous phyllites in the reclined lamego fold in which the cabeca de pedra orebody represents the hinge zone mineralization is concentrated in silicification zones and their quartz veins as well as in sulfide minerals product of bif sulfidation hydrothermal alteration varies according to host rock with abundant sulfide carbonate in bif and sericite chlorite in carbonaceous phyllite quartz vein classification according to structural relationships and host rocks identified three vein systems the v1 system mainly composed of smoky quartz qtz i and pyrite is extensional crosscuts the bedding plane s0 of bif and is parallel to the fold axis the v2 system of the same composition is represented by veins that are parallel to the s1 2 foliation and s0 this system is also characterized by silicification zones in the bif carbonaceous phyllite contact that has its maximum expression in the hinge zone of folds the v3 system has milky quartz qtz ii veins which result from the recrystallization of smoky quartz located mainly in shear zones and faults these veins form structures en echelon and vein arrays the most common ore minerals are pyrite as pyrite and arsenopyrite fluid inclusion fi trapped in all quartz veins present composition in the h2o co2 ch4 nacl system fluid evolution can be interpreted in two stages i aqueous carbonic fluid trapped in qtz i of low salinity 2 equiv wt nacl and ii carbonic aqueous fluid of moderate salinity average 9 eq wt nacl hosted in qtz ii both stages are characterized by decrepitation temperatures in the range of 200 to 300 c and suggest a fluid of metamorphic origin applying an arsenopyrite geothermometer the calculated formation temperature for the cabeca de pedra orebody is 300 to 375 c the vertical intersection of the isochors allows a minimum pressure calculation of 2 6 kbar the composition of individual fis of this orebody obtained by la icp ms analyses compared with results of fis for the carvoaria velha deposit corrego do sitio lineament highlights a standard composition typical of metamorphic fluids with na k ca mg which increase or decrease in concentration as a function of salinity in both deposits trace elements vary according to fluid rock reactions and are directly related to the host rock composition the comparison of data sets of the two deposits shows that the cabeca de pedra fis have a higher enrichment in zn while cu as and sb are richer in carvoaria velha suggesting influence of the host rock geochemistry the suggested mechanisms for gold precipitation at the cabeca de pedra orebody lamego gold deposit are i hydrolysis of the carbonaceous matter of phyllite and bif affecting fo2 destabilizing sulfur complexes and enhancing gold precipitation ii replacement of bif iron carbonates by sulfides and iii continuous pressure changes that lead to silica precipitation and free gold other than playing the long recognized role of the carbonaceous phyllites as a fluid barrier the data highlight their importance as a source of metals

high quality surface microseismic data illuminates fracture treatments a case study in the montney monitoring hydraulic fracture stimulations from the surface is a technique that in the past met with mixed success one reason for this experience is that the measurement has often been treated as if it were only a minor variant of the reflection surveys our industry is most familiar with while reflection seismic sources are designed to generate primarily p waves fracturing rocks emit both p and s waves with the much larger proportion of energy as s waves to capture the information content in the microseismic wavefield surveys must be designed to record and processing strategies designed to use the full vector wavefield energy emitted by the fracture process to record the full vector wavefield requires the use of appropriate sensors capable of recording low frequencies and three components

does gold in orogenic deposits come from pyrite in deeply buried carbon rich sediments insight from volatiles in fluid inclusions the origin of volatiles in fluid inclusions was reviewed for testing the involvement at depth of carbonaceous pyritic sedimentary rocks as the source for orogenic gold mineralization fluid inclusions from selected deposits were analyzed by solid probe mass spectrometry fluids are mostly aqueous carbonic with variable amounts of n 2 ch 4 c 2 h 6 ar h 2 s h 2 and he for fluids with ch 4 and c 2 h 6 their ratios c 1 c 2 range from 2 6 to 25 5 indicating that c 2 h 6 is sourced from thermally degraded organic matter proportions of co 2 ch 4 c 2 h 6 and h 2 are highly variable and can be explained by hydrothermal reactions where c 2 h 6 is degraded to co 2 by water consumption such reactions may account for the problematic co 2 rich h 2 o poor fluids associated with some of the richest gold districts conditions needed for c 2 h 6 degradation are also fundamental for forming gold deposits such as hs enriched fluids for carrying gold and local weakly oxidizing conditions for promoting gold precipitation the c 2 h 6 content is recorded in fluids from mesoarchean to cretaceous gold deposits providing support for a general model where fluids and gold were sourced from deeply buried carbon rich and pyrite gold bearing sedimentary rocks

precise inversion of logged slownesses for elastic parameters in a gas shale formation abstractdipole sonic log data recorded in a vertical pilot well and the associated production well are analyzed over a 200 1100 ft section of a north american gas shale formation the combination of these two wells enables angular sampling in the vertical direction and over a range of inclination angles from 54 to 90 dipole sonic logs from these wells show that the formation s average properties are to a very good approximation explained by a transversely isotropic medium with a vertical symmetry axis and with elastic parameters satisfying c13 c12 but inconsistent with the additional annie relation c13 c33 2c55 more importantly these data clearly show that at least for fast anisotropic formations such as this gas shale sonic logs measure group slownesses for propagation with the group angle equal to the borehole inclination angle conversely the data are inconsistent with an interpretation that they measure phase slownesses for propagation with the phase angle equal to the borehole inclinatio

n2 and co2 in deep crustal fluids evidence from the caledonides of norway abstract high pressure metamorphic rocks eclogites and high pressure granulites occur along the entire length of the norwegian caledonides and have formed from a variety of protoliths in some cases the relationship between protoliths high pressure rocks and their later retrogression products have been preserved in situ fluid inclusion data suggest a simple correlation between metamorphic grade and metamorphic fluid composition 1 eclogites and high pressure granulites contain n 2 bearing fluids pure n 2 or mixtures with co 2 or h 2 o with x n 2 5 in some eclogite facies rocks co 2 1bn 2 inclusions are associated with aqueous brine inclusions ca 30 wt nacl the two compositions representing immiscible fluids at peak metamorphic conditions 2 granulite facies protoliths and eclogites reworked in the granulite facies contain pure co 2 or co 2 dominated fluids with less than 2 5 n 2 3 rocks retrograded in the amphibolite facies contain h 2 o 1bnacl fluids immiscibility between brine and anhydrous n 2 1bco 2 fluid and between anhydrous fluid and waterbearing aluminosilicate melt have taken place in some eclogites during high grade metamorphism nitrogen may be incorporated in minerals as nh 4 substituting for k or it may occur as n 2 in the free fluid phase the partitioning of nitrogen between minerals and fluids depends upon the water activity and oxygen fugacity during metamorphism low a h 2 o and or high f o 2 partitioning nitrogen to the fluid phase a rock interacting with a carbonic fluid at granulite facies pt conditions will be depleted in mineralogically bound nitrogen in cases where the protoliths of high pressure rocks have been through a previous granulite facies event a local source for the nitrogen contained in high pressure fluid is therefore unlikely

characteristics of crushed rocks observed in drilled cores in landslide bodies located in accretionary complexes abstract the recent development of high quality boring which uses foam surfactants has made it possible to examine the detailed geological constitution and structure of landslide bodies however geological information related to landslides has not been obtained appropriately even from undisturbed high quality drilled cores moreover it has been difficult to distinguish between rocks crushed by landslide movement and the fault breccia in accretionary complexes we examined the detailed geology of high quality drilled cores of landslide bodies on the shimanto belt and the chichibu belt the fault breccia near the landslide bodies was found to exhibit planar fabrics while the crushed breccias in the landslide bodies showed a random fabric we discovered that classifying the degree of crushing and inspecting the planar fabrics of rocks are effective in the geological determination of landslide bodies

formation of the campbell red lake gold deposit by h 2 o poor co 2 dominated fluids the campbell red lake gold deposit in the red lake greenstone belt with a total of approximately 840 t of gold past production reserves and an average grade of 21 g t au is one of the largest and richest archean gold deposits in canada gold mineralization is mainly associated with silicification and arsenopyrite that replace carbonate veins breccias and wallrock selvages the carbonate veins and breccias which are composed of ankerite quartz and characterized by crustiform cockade textures were formed before and or in the early stage of penetrative ductile deformation whereas silicification arsenopyrite replacement and gold mineralization were coeval with deformation microthermometry and laser raman spectroscopy indicate that fluid inclusions in ankerite and associated quartz q1 and main ore stage quartz q2 are predominantly carbonic composed mainly of co2 with minor ch4 and n2 aqueous and aqueous carbonic inclusions are extremely rare in both ankerite and quartz h2o was not detected by laser raman spectroscopic analyses of individual carbonic inclusions and by gas chromatographic analyses of bulk samples of ankerite and main ore stage quartz q2 fluid inclusions in post mineralization quartz q3 are also mainly carbonic but proportions of aqueous and aqueous carbonic inclusions are present trace amounts of h2s were detected by laser raman spectroscopy in some carbonic inclusions in q2 and q3 and by gas chromatographic analyses of bulk samples of ankerite and q2 3he 4he ratios of bulk fluid inclusions range from 0 008 to 0 016 ra in samples of arsenopyrite and gold homogenization temperatures th co2 of carbonic inclusions are highly variable from 4 1 to 30 4 c mostly to liquid some to vapor but the spreads within individual fluid inclusion assemblages fias are relatively small within 0 5 to 10 3 c carbonic inclusions occur both in fias with narrow th co2 ranges and in those with relatively large th co2 variations the predominance of carbonic fluid inclusions has been previously reported in a few other gold deposits and its significance for gold metallogeny has been debated some authors have proposed that formation of the carbonic fluid inclusions and their predominance is due to post trapping leakage of water from aqueous carbonic inclusions h2o leakage model whereas others have proposed that they reflect preferential trapping of the co2 dominated vapor in an immiscible aqueous carbonic mixture fluid unmixing model or represent an unusually h2o poor co2 dominated fluid single carbonic fluid model based on the fia analysis reported in this study we argue that although post trapping modifications and host mineral deformation may have altered the fluid inclusions in varying degrees these processes were not solely responsible for the formation of the carbonic inclusions the single carbonic fluid model best explains the extreme rarity of aqueous inclusions but lacks the support of experimental data that might indicate the viability of significant transport of silica and gold in a carbonic fluid in contrast the weakness of the unmixing model is that it lacks unequivocal petrographic evidence of phase separation if the unmixing model were to be applied the fluid prior to unmixing would have to be much more enriched in carbonic species and poorer in water than in most orogenic gold deposits in order to explain the predominance of carbonic inclusions the h2o poor co2 dominated fluid may have been the product of high grade metamorphism or early degassing of magmatic intrusions or could have resulted from the accumulation of vapor produced by phase separation external to the site of mineralization

behavior of a landslide prior to inducing a viaduct failure caracas la guaira highway venezuela a reactivation of a large ancient landslide identified in 1987 began to progressively damage the southern side of an important prestressed concrete span structure of a highway connecting caracas capital of venezuela with its main port and airport this paper deals with the behavior of the landslide over a period of 19 years and the final failure of the structure in march 19 2006 results of geotechnical investigation evaluation of inclinometer readings and surface control point displacements as well as behavior of the structure subjected to the slide thrust are discussed several causes that may explain the reactivation and behavior of the landslide and some aspects about failure time prediction are also described

genesis of the selinsing gold deposit peninsular malaysia constraints from mineralogy geochemistry and in situ sulfur isotope compositions of sulfides abstract as a renowned orogenic lode gold deposit the selinsing gold deposit is located in the central belt of peninsular malaysia geologically the gold deposit is characterized by auriferous quartz veins and fine grained gold minerals coexisted with sulfides and the ore body is hosted by low grade metamorphic sedimentary rocks and volcanic rocks furthermore gold mineralization is closely related to tectonic deformation four main stages of vein formation have been identified namely 1 quartz pyrite arsenopyrite vein 2 quartz pyrite gold vein 3 quartz stibnite pyrite vein and 4 quartz chlorite vein the occurrence of gold includes two types i e visible gold and invisible gold the former is featured by coarse grained gold millimeter scale such as auriferous quartz veins and fine grained gold micron scale such as native gold calaverite and electrum the latter is contained in pyrite and arsenopyrite in the form of nano scale native gold particles au0 and lattice gold au1 the geothermometer of arsenopyrite and chlorite as well as temperature sulfur fugacity diagram indicate that the temperature and sulfur fugacity of hydrothermal fluid decrease gradually considering that the sulfur fugacity drops gradually and aqueous inclusions coexist with carbonic inclusions it is inferred that sulfuration reaction in which sulfur is consumed to produce sulfides and fluid immiscibility or phase separation may be responsible for gold precipitation tested by la mc icp ms the in situ sulfur isotope compositions of sulfides formed in different stages are homogenous about 1 to 1 and the calculated h2s dominated hydrothermal fluid is also consistent about 2 to 0 in sulfur isotope compositions which reflect the mantle or ultrabasic rock and basic rock or magmatic rocks may be a potential source of sulfur combined with possible source and tectonic evolution of peninsular malaysia possible metallogenic processes are proposed to explain genesis of the selinsing gold deposit and other gold deposits in the central belt i e ore forming fluid was differentiated from oceanic crust and or fertilized mantle wedge or ore forming fluid may be sourced from concealed magmatic rocks that formed by subduction of the palaeo tethys toward the east malaysia block

the reliability of microseismic moment tensor solutions surface versus borehole monitoring abstractsource mechanisms of microseismic events resolved as moment tensor solutions usually are obtained using either surface monitoring arrays which appear to obtain mechanisms with high shear components or borehole arrays which tend to constrain more variable mechanisms with higher tensile components however the corresponding reliability of the solutions remains unclear synthetic tests are therefore conducted to compare the reliability of moment tensor solutions from surface and two and three well borehole arrays based purely on geometry moment tensor inversion is carried out for synthetically generated amplitudes with added random noise and the bias and variance in the solutions are calculated for the surface array all inversions are able to constrain reliable results with negligible bias and low variance whereas borehole geometries with two wells produce reliable results only when including p and s wave amplitudes recorded on three components in the inversion as is usual surface a

petroleum reservoir characterization using downhole microseismic monitoring imaging of microseismic data is the process by which we use information about the source locations timing and mechanisms of the induced seismic events to make inferences about the structure of a petroleum reservoir or the changes that accompany injections into or production from the reservoir a few key projects were instrumental in the development of downhole microseismic imaging most recent microseismic projects involve imaging hydraulic fracture stimulations which has grown into a widespread fracture diagnostic technology this growth in the application of the technology is attributed to the success of imaging the fracture complexity of the barnett shale in the fort worth basin texas and the commercial value of the information obtained to improvecompletions and ultimately production in the field the use of commercial imaging in the barnett is traced back to earlier investigations to prove the technology with the cotton valley imaging project and earlier experiments at the m site in the piceance

archean gold mineralization and oxidized hydrothermal fluids sulfate minerals hematite and isotopically fractionated sulfides are relatively rare in rocks of archean age several archean au deposits however contain one or more of these features indicative of oxidized hydrothermal fluids they include hemlo mcintyre hollinger macassa lake shore and ross which are all in ontario canada and kalgoorlie in australia examples of lesser deposits are in hislop township and in the matachewan area ontario canada with the exception of hemlo these are quartz carbonate vein deposits spatially and temporally associated with felsic plutonism because metamorphic fluids and archean surface waters were mostly reducing the most feasible general source for the fluids was felsic magmas parent magmas were relatively oxidized hydrous and co 2 rich the oxidized character may have favored the incorporation of au into the partial melt and its partitioning into magmatic aqueous fluids high contents of co 2 are conducive to the separation of an aqueous fluid from magma at greater depth than otherwise fluid inclusion data support the formation of major archean au vein deposits at deeper crustal levels than more recent magmatic hydrothermal mineralization such as porphyry cu deposits co 2 rich fluids can unmix into two phases at relatively high temperatures and pressures a saline aqueous liquid and a low salinity h 2 o co 2 liquid this can cause partitioning of cl complexed base metals from other metals including au sb and as the extensive carbonatization around most deposits has consistent delta 13 c values in the range of juvenile magmatic co 2

an atmospheric source of s in mesoarchaean structurally controlled gold mineralisation of the barberton greenstone belt abstract the barberton greenstone belt of southern africa hosts several mesoarchaean gold deposits the ores were mostly formed in greenschist facies conditions and occur as hydrothermal alteration zones around extensional faults that truncate and post date the main compressional structures of the greenstone belt ore deposition was accompanied by the intrusion of porphyries which has led to the hypothesis that gold may have been sourced from magmas because the transport of au in the hydrothermal fluids is widely believed to have involved s complexes tracing the origin of s may place strong constraints on the origin of au we measured multiple s isotopes in sulfide ore from sheba and fairview mines of the barberton greenstone belt to distinguish deep s sources e g magmas from surface s sources i e rocks of the volcano sedimentary succession that contain s processed in the atmosphere preserved as sulfide and sulfate minerals ion probe sims analyses of pyrite from ore zones indicate mass independent fractionation of s isotopes 33s 0 6 to 1 0 and the distribution of the analyses in the 33s 34s space matches the distribution peak of previously published analyses of pyrite from the entire volcano sedimentary succession notwithstanding that the h2o co2 components of the fluids may have been introduced from a deep source external to the greenstone belt rocks the fact that s bears an atmospheric signature suggests the hypothesis that the source of au should also be identified in the supracrustal succession of the greenstone belt our findings differ from conclusions of previous studies of other archaean shear hosted au deposits based on mineralogical and isotopic evidence which suggested a magmatic or mantle source for au and imply that there is no single model that can be applied to this type of mineralisation in the archaean

discriminating fluid source regions in orogenic gold deposits using b isotopes abstract the genesis of orogenic gold deposits is commonly linked to hydrothermal ore fluids derived from metamorphic devolatilization reactions however there is considerable debate as to the ultimate source of these fluids and the metals they transport tourmaline is a common gangue mineral in orogenic gold deposits it is stable over a very wide p t range demonstrates limited volume diffusion of major and trace elements and is the main host of b in most rock types we have used texturally resolved b isotope analysis by secondary ion mass spectrometry sims to identify multiple fluid sources within a single orogenic gold ore district the loulo mining district in mali west africa hosts several large orogenic gold ore bodies with complex fluid chemistry associated with widespread pre ore na and multi stage b metasomatism the gara deposit as well as several smaller satellites formed through partial mixing between a dilute aqueous carbonic fluid and a hypersaline brine hydrothermal tourmaline occurs as a pre ore phase in the matrix of tourmalinite units which host mineralization in several ore bodies clasts of these tourmalinites occur in mineralized breccias disseminated hydrothermal and vein hosted tourmaline occur in textural sites which suggest growth during and after ore formation tourmalines show a large range in 11 b values from 3 5 to 19 8 which record a change in fluid source between paragenetic stages of tourmaline growth pre mineralization tourmaline crystals show heavy 11 b values 8 19 8 and high x site occupancy na ca 0 69 1 apfu suggesting a marine evaporite source for hydrothermal fluids syn mineralization and replacement phases show lighter 11 b values 3 5 to 15 1 and lower x site occupancy 0 62 0 88 apfu suggesting a subsequent influx of more dilute fluids derived from devolatilization of marine carbonates and clastic metasediments the large overlapping range in isotopic compositions and a skew toward the opposing population in the 11 b data for both tourmaline groups reflects continual tourmaline growth throughout mineralization which records the process of fluid mixing a peak in 11 b values at 8 largely controlled by tourmalines of syn to post ore timing represents a mixture of the two isotopically distinct fluids this paper demonstrates that b isotopes in tourmaline can be instrumental in interpreting complex and dynamic hydrothermal systems the importance of b as an integral constituent of orogenic ore forming fluids and as a gangue phase in orogenic gold deposits makes b isotope analysis a powerful tool for testing the level of source region variability in these fluids and by extension that of metal sources

structural analysis and metamorphism of the barlow fault zone chibougamau area neoarchean abitibi subprovince implications for gold mineralization faults and deformation zones are important features of archean terranes because of their significance for structural evolution and the formation of large gold districts in the chibougamau area no

long term gravitational deformation of rocks by mass rock creep abstract subsurface rocks beneath slopes are deformed to various degrees in various ways by mass rock creep mrc when they are subjected to a gravitationally unstable state for a long period mrc forms folds faults and numerous kinds of fractures such deformation is one of the main factors for deteriorating rock masses on slopes and also precursors of many landslides mrc deformations which have often been ascribed to tectonic origins can be distinguished from tectonic ones by their deformational features landforms and relationships between slope morphology and subsurface structures mrc folds are flexural slip folds that have the following mesoscopic to microscopic characteristics their axial surfaces are not smooth but are jagged and many visible openings or open fractures develop in association with the folds the jagged axial surfaces become smoother at depth and openings decrease in width with increasing overburden at the deformation site macroscopic types of mrc folds change according to the relationship between foliations and slopes buckling folds form in consequent slopes drag folds form in a deeper part of obsequent slopes and bending folds form in slopes with steep dipping foliations consequent or obsequent by downslope bowing of foliations shear fractures and tension fractures are the main deformational structures formed by mrc in massive rocks among shear fractures those of listric origin are remarkable tension fractures in general occur either in networks dividing rocks into fragments that slip and rotate irregularly in relation to each other or in parallel arrays of steeply dipping fractures an mrc fault has a shear zone consisting of a pulverized zone with gouge and a phyllitic or brecciated zone in a densely foliated rock the phyllitic zone is formed by microscopic slip along foliations in a sparsely foliated rock the brecciated zone is formed by random crushing except for the faults made through the shear fractures in massive rocks landforms due to mrc are gentle slopes bounded by horseshoe knicklines upslope convex slopes ridge top depressions multiple ridges uphill facing scarps and ridge crossing depressions

origin of the co2 only fluid inclusions in the palaeoproterozoic carara vein quartz gold deposit ipitinga auriferous district se guiana shield brazil implications for orogenic gold mineralisation abstract the carara gold deposit located in the ipitinga auriferous district south eastern portion of the guiana shield northern brazil is a typical orogenic greenstone hosted auriferous quartz vein mineralisation was post metamorphic and syn tectonic in relation to the host palaeoproterozoic ca 2 03 ga shear zone developed close to the tectonic boundary between a palaeoproterozoic continental arc and an archaean block the deposit style is very simple consisting of a quartz vein and its hydrothermal envelope which is composed of muscovite and tourmaline sulphides are rare muscovite and tourmaline in addition to gold fill small fractures in the quartz vein the fluid inclusion assemblage trapped in high and low grade portions of the au quartz vein is rather enigmatic consisting of one phase co 2 inclusions with no visible water at room or sub zero temperatures although small amounts of water have been detected by micro raman analysis in this aspect carara differs from the other gold showings in the same district which are characterized by abundant aqueous carbonic fluid inclusions the carbonic fluid is composed predominantly of co 2 in addition to 2 and traces of ch 4 and c 2 h 6 the carbonic fluid show very variable densities which is interpreted to result from post entrapment re equilibration inclusions in the high grade quartz are the densest 0 89 to 1 07 g cm 3 and with less effects of re equilibration these inclusions approximate the physico chemical characteristics of the parental fluid that started to be trapped at least around the amphibolite facies metamorphic conditions and then followed a retrograde path most of the inclusions appear to have been trapped and or re equilibrated at 350 to 475 c and 1 8 to 3 6 kbar which implies a 7 to 12 km depth of vein formation and gold mineralisation both phase separation of a carbonic aqueous fluid x co 2 0 8 and the existence of an originally co 2 dominated fluid could account for the observed fluid inclusion properties and the absence of h 2 o bearing inclusions in the mineralised vein the fluid inclusion characteristics combined with published geological and isotopic information indicate a deep seated source for co 2 that could be mantle magmatic or metamorphic in origin we suggest that the likely sources are fluid produced by the 2 07 ga old charnockites that occur in the region and or the coeval high grade metamorphism that is widespread in the guiana shield

inversion for parameters of tensile earthquakes the tensile source model generalizes the shear source model by assuming that the slip vector can be arbitrarily oriented with respect to the fault and is not constrained to lie within the fault plane the proposed inversion for the parameters of tensile sources is based on the evaluation of the isotropic iso compensated linear vector dipole clvd and double couple dc components in seismic moment tensors the most significant parameters inverted are the ratio at the fault denoted as the parameter and the inclination of the slip vector from the fault the parameter is significant for discriminating noisy moment tensors of shear earthquakes from those of tensile earthquakes the inclination can be accurately determined from the dc component in the moment tensor because the dc component rapidly decreases with increasing for example the inclination of 20 causes dc being 50 60 only the inversion is applied to earthquakes which occurred in january 1997 in west bohemia czech republic it is shown that some of these earthquakes display tensile faulting the parameter is 0 1 the inclination of the slip from the fault attains values of up to 20 this inclination is a result of tensile traction and reduced shear traction along the fault and high fluid pressure in the region

high co2 content of fluid inclusions in gold mineralisations in the ashanti belt ghana a new category of ore forming fluids a reply fluid inclusions were studied in samples from the ashanti konongo southern cross prestea abosso damang and ayanfuri gold deposits in the ashanti belt ghana primary fluid inclusions in quartz from mineralised veins of the ashanti prestea konongo southern cross and abosso damang deposits contain almost exclusively volatile species the primary setting of the gaseous i e the fluid components co2 ch4 and n2 fluid inclusions in clusters and intragranular trails suggests that they represent the mineralising fluids microthermometric and raman spectroscopic analyses of the inclusions revealed a co2 dominated fluid with variable contents of n2 and traces of ch4 water content of most inclusions is below the detection limits of the respective methods used aqueous inclusions are rare in all samples with the exception of those from the granite hosted ayanfuri mineralisation here inclusions associated with the gold mineralisation contain a low salinity co2 and low salinity 6 eq wt nacl however fluid inclusions in quartz from the gold mineralisations in the ashanti belt point to distinctly different fluid compositions specifically the predominance of co2 and co2 h2o have to be emphasized fluid systems with this unique bulk composition were apparently active over more than 200 km along strike of the ashanti belt fluids rich in co2 may present a hitherto unrecognised new category of ore forming fluids

a biogeochemical influence on the secular distribution of orogenic gold orogenic gold deposits are unevenly distributed in geologic time the richest period of orogenic gold deposit formation was the phanerozoic which followed a 1 b y period of relatively meager deposit generation during the proterozoic this proterozoic low gold period developed despite continent building episodes which should have been appropriate for orogenic gold genesis here a brief review of the changes in global geochemistry brought on by evolving interactions between plate tectonics and the biosphere is conducted before the consequences for gold uptake into sedimentary pyrite are discussed it is suggested that the extensive oxygenation of the deep oceans during the second great oxidation event over the period 635 to 510 ma produced conditions where gold was soluble in the deep oceans from that point on regions where bacterial sulfate reduction drove formation of sedimentary pyrite also destabilized this soluble gold promoting its uptake into pyrite and allowing formation of metallogenically enhanced sedimentary sequences these sediments would have become ideal source rocks for gold deposits during subsequent collisional tectonics and metamorphism this biogenic influence on source region enhancement may explain the association during the phanerozoic eon between some of the world s most gold productive regions and sedimentary sequences that contain pyritic carbonaceous rocks

shear wave group velocity surfaces in low symmetry anisotropic media abstractshear waves excited by natural sources constitute a significant part of useful energy recorded in downhole microseismic surveys in rocks such as fractured shales exhibiting symmetries lower than transverse isotropy ti the shear wavefronts are always multivalued in certain directions potentially complicating the data processing and analysis this paper discusses a basic tool the computation of the phase and group velocities of all waves propagating along a given ray that intends to facilitate the understanding of geometries of the shear wavefronts in homogeneous anisotropic media with this tool arbitrarily complex group velocity surfaces can be conveniently analyzed providing insights into possible challenges to be faced when processing shear waves in anisotropic velocity models that have symmetries lower than ti among those challenges are complicated multipathing and the presence of cones of directions known as internal refraction cones in which no fast shear waves propagate and t

microseismic moment tensors a path to understanding frac growth microseismic monitoring is a valuable tool in understanding the efficacy of hydraulic fracture treatments determination of event locations and magnitudes leads to estimations of the geometry of the fracture zone and certain dynamics of the fracturing process with sufficient resolution the hypocenters may even reveal failure planes or other underlying structures controlling the distribution of events and of interest to petroleum engineers to test various hypotheses on fracture growth

beyond the dots in the box microseismicity constrained fracture models for reservoir simulation summary monitoring of induced microseismic events usually results in locations for these events and a geometrical interpretation of these dots in the box in this study we show how additional information obtained from observed microseismic events namely the source mechanisms were used to generate a discrete fracture network using the wide aperture of a surface star like array fracstar allows inversion for both shear and non shear source mechanisms both volumetric and shear only source mechanism inversion was carried out on microseismic events from the treatment of a shale gas reservoir in the continental us during the same hydraulic fracture stimulation treatment both dip slip and reverse faulting sources were active in this reservoir the source mechanisms revealed fracture orientations more accurately than could be inferred from microseismic event locations alone the activity associated with different mechanisms is interpreted as indicating reactivation of existing fractures in the rock as well as suggesting generation of new fractures failure analysis using source mechanisms on individual events allows an integrated understanding of the complex fracture interactions taking place in the reservoir and also provides a more complete understanding of the stress conditions in the reservoir during the treatment fracture orientations locations and failure mechanisms are translated into discrete fracture network dfn models that can be used to verify the extent and character of the fractures created or reactivated during the fracture treatment and may ultimately be used to generate fracture flow properties for reservoir simulation

gold in iron oxide copper gold deposits abstract iron oxide copper gold iocg deposits contain economic or anomalous gold and the gold distribution is important both for its economic significance and ore genesis however the gold distribution in iocg deposits and its controlling factors remain unclear the gold grades and tonnages of selected thirty six deposits in some well defined iocg provinces are compiled in this paper the gold grades in these iocg deposits range from 0 01 to 1 41 g t averaging 0 41 g t and 90 of them are less than 1 g t the gold tonnages range from 0 6 to 483 t averaging 64 t but with the exception of the giant olympic dam containing gold of 2968 t the cu au ratios of iocg deposits are significantly variable ranging from 0 7 to 64 but most values fall between 1 0 and 6 0 the gold is present in three forms 1 native gold 2 electrum and 3 gold bismuth antimony tellurium alloy the gold distribution is controlled by gold contents in host rocks and the efficiency of precipitation mechanism e g cooling fluid rock interaction and fluid mixing in order to find gold rich iocg deposits at province scale the most important thing is to focus on areas both with gold enriched host rocks and efficient depositional mechanism and at a deposit scale the exploration of gold rich deposits should also focus on low temperature deposits

mobility of gold during metamorphism of the dalradian in scotland abstract mobility of au and related metals during metamorphism has been suggested to be the source of metals enriched in orogenic au deposits this study investigates the mobility of au as and sb during metamorphism of the dalradian metasedimentary rocks of scotland the metamorphic processes in the dalradian of scotland are extremely well studied and the terrane is an ideal area to investigate mobility of these metals our results show that of the 25 major and trace elements analysed only au as sb s and volatile contents as shown by loss on ignition loi values show systematic variation with the metamorphic grade of the samples average au concentrations decrease from 1 1 0 55 ppb and 0 72 0 34 ppb in chlorite and biotite zone rocks down to 0 4 0 22 ppb and 0 34 0 13 ppb in kyanite and sillimanite zone rocks average as concentrations decrease from 4 8 ppm range 0 5 to 17 8 ppm and 1 96 1 9 ppm in chlorite and biotite zone rocks down to 0 24 0 15 ppm and 0 2 0 12 ppm in kyanite and sillimanite zone rocks average sb concentrations decrease from 0 18 0 15 ppm and 0 11 0 10 ppm in chlorite and biotite zone rocks down to 0 04 0 02 ppm in both kyanite and sillimanite zone rocks sulphur and loi concentrations also show significant decreases mass balance calculations indicate that compared to chlorite and biotite zone samples sillimanite zone samples have an average mass loss of 62 14 94 4 and 74 14 for au as and sb respectively every 1 km3 of chlorite biotite zone mixed psammitic pelitic protolith rock that is metamorphosed to sillimanite zone conditions would release 1 5 t au 8613 t as 270 t sb and 1 02 mt s the mobility of these elements is strongly controlled by the paragenesis of sulphide minerals pyrite sphalerite galena and cobaltite as well as gersdorffite decrease in abundance with increasing metamorphic grade in the dalradian metasedimentary rocks a critical aspect of the sulphide paragenesis is the transition of pyrite to pyrrhotite this transition is complete by mid greenschist facies in the loch lomond samples but is more gradual at glen esk occurring between biotite and sillimanite zones the au as and sb content of the sulphide assemblage also decreases with increasing metamorphic grade and we suggest that this is a controlling factor on the mobility of these metals from the dalradian metasedimentary rocks during metamorphism chlorite may be an important host mineral for as in the greenschist facies rocks breakdown of chlorite indirectly drives the mobility of au as and sb as this produces the bulk of metamorphic fluid that drives transition between pyrite and pyrrhotite we suggest that there is potential for significant undiscovered mineralisation in the central and sw highlands of scotland however as the total mass of gold mobilised is lower than observed in other metasedimentary terranes such as the otago and alpine schist s new zealand very efficient fluid focussing and trapping mechanisms would be required to form large deposits in the dalradian of scotland

towards producing mineral resource potential maps within a mineral systems framework with emphasis on australian orogenic gold systems abstract discovery of new deposits has slowed dramatically since the beginning of the 21st century despite increased expenditure targeting below deep complex cover is recognised as key to opening up new search spaces and re invigorating exploration success existing techniques and technologies are reaching maturity as direct detection exploration methods are costly and have limited success when targeting beneath cover thus the application of a predictive conceptual based approach to exploration targeting is required the mineral systems concept provides a framework within which the critical elements of a system can be defined and incorporated into a predictive exploration targeting model however modelling of entire mineral systems remains in its infancy as such the effective translation of the mineral systems concept into robust targeting models is defined as a significant research challenge by several authors a conceptual whole system modelling approach is proposed in light of the critical elements of an orogenic gold mineralising system and a review of existing exploration tools the approach combines probabilistic sub models for predicting total mineral endowment with localised mineral distribution linking resource endowment assessments total mineral endowment with fluid dynamics and fluid rock interaction modelling local mineral distribution provides an opportunity to develop resource potential maps that define the approximate cost benefit of exploring any given location further research is required for such modelling methods to become feasible although hydrodynamic and hydrogeologic modelling has advanced in other research fields methods for modelling auriferous fluid flow through the crust remain under developed this in part is due to detailed 3d geological data being unavailable or prohibitively expensive to acquire potential solutions to limited data availability include the development of more advanced interpolation and geophysical inversion methodologies based on data from well understood geological provinces resulting in improved 3d geological interpretations collaboration between academia and the minerals industry to develop an integrated approach to entire mineral system modelling may lead to successful predictive exploration by providing a meaningful output to guide decision making during the exploration targeting process

shear strength of soils containing amorphous clay size materials in a slow moving landslide abstract the shear behavior of soils rich in amorphous clay size materials was not well reported in the literature this study analyzed the direct shear and ring shear test data of soil samples containing 55 74 amorphous materials in the clay fraction from a slow moving landslide in eastern honolulu hi the direct shear test results showed that the undisturbed soil samples when not sheared internally had peak cohesion c of about 50 kpa and internal friction angle o of about 10 this implies that the amorphous clay size materials provided strong interparticle bonds for the soils breaking of the bonds during the softening process and redistribution of the amorphous clay size materials were primarily responsible for the drop from the peak strength to the residual strength c 0 o 10 from back calculation with slope w and c 0 o 5 7 from the ring shear test the drained residual failure envelope is stress dependent due to the interaction of the gel like amorphous clay size materials with crystalline silt and sand sized particles the amorphous clay size materials act as the contact between crystalline particles the contact increases with increasing consolidation stress resulting in a decrease in the shear strength and the residual friction angle

earthquake mechanisms from linear programming inversion of seismic wave amplitude ratios the amplitudes of radiated seismic waves contain far more information about earthquake source mechanisms than do first motion polarities but amplitudes are severely distorted by the effects of heterogeneity in the earth this distortion can be reduced greatly by using the ratios of amplitudes of appropriately chosen seismic phases rather than simple amplitudes but existing methods for inverting amplitude ratios are severely nonlinear and require computationally intensive searching methods to ensure that solutions are globally optimal searching methods are particularly costly if general moment tensor mechanisms are allowed efficient linear programming methods which do not suffer from these problems have previously been applied to inverting polarities and wave amplitudes we extend these methods to amplitude ratios in which formulation on inequality constraint for an amplitude ratio takes the same mathematical form as a polarity observation three component digital data for an earthquake at the hengill grensdalur geothermal area in southwestern iceland illustrate the power of the method polarities of p sh and sv waves unusually well distributed on the focal sphere cannot distinguish between diverse mechanisms including a double couple amplitude ratios on the other hand clearly rule out the double couple solution and require a large explosive isotropic component

inversion of microseismic data for triclinic velocity models modern downhole microseismic surveys often employ geometries in which ray trajectories generated by a collection of locatable events provide full polar and azimuthal coverage making it possible to estimate the in situ seismic anisotropy we show that traveltimes and particle motions of the direct p and shear waves acquired in such geometries can constrain stiffness tensors of triclinic media while obtaining all 21 stiffness coefficients of a homogeneous triclinic space simultaneously with locating pertinent microseismic events from data recorded in a single vertical well is relatively straightforward the same methodology does not necessarily succeed in layered formations because the combination of their vertical heterogeneity and azimuthal anisotropy might invalidate the commonly adopted approximation of the event azimuths by those of the p wave polarization vectors when the event azimuths cannot be derived from the particle motions traveltimes observed in two or more wells are required to locate the events and build layered triclinic or higher symmetry azimuthally anisotropic velocity models as our numerical tests indicate the multi well event location methods are expected to perform better than their single well counterparts because they rely solely on triangulation and eliminate the usually pronounced azimuthal uncertainties in the event locations that stem from noises adversely affecting hodogram analysis

pyrite deformation and connections to gold mobility insight from micro structural analysis and trace element mapping abstract the metamorphic transition of pyrite to pyrrhotite results in the liberation of lattice bound and nano particulate metals initially hosted within early sulphide minerals this process forms the basis for the metamorphic driven au upgrading model applied to many orogenic au deposits however the role of syn metamorphic pyrite deformation in controlling the retention and release of au and related pathfinder elements is poorly understood the lower amphibolite facies metamorphic mineral assemblage act bt pl ep alm cal qz ilm 550 c of canada s giant detour lake deposit falls within the range of pressure temperature conditions 450 c for crystal plastic deformation of pyrite we have applied a complementary approach of electron backscatter diffraction ebsd mapping and laser ablation inductively coupled plasma mass spectrometry la icp ms 2d element mapping on pyrite from the detour lake deposit chemical element maps document an early generation of au rich sieve textured pyrite domains and a later stage of syn metamorphic oscillatory zoned au poor pyrite both pyrite types are cut by au rich fractures as a consequence of remobilization of au with trace element enrichment of first row transition elements post transition metals chalcogens and metalloids during a late brittle deformation stage however similar enrichment in trace elements and au can be observed along low angle grain boundaries within otherwise au poor pyrite indicating that heterogeneous microstructural misorientation patterns and higher strain domains are also relatively au rich we therefore propose that the close spatial relationship between pyrite and au at the microscale features typical of orogenic au deposits reflects the entrapment of au within deformation induced microstructures in pyrite rather than the release of au during the metamorphic transition from pyrite to pyrrhotite moreover mass balance calculations at the deposit scale suggest that only a small percentage of au could have been sourced from pyrite and instead point to the role of substructures in pyrite as depositional traps for au during syn metamorphic deformation and fluid assisted diffusion au upgrading

multi stage and multi sourced fluid and gold in the formation of orogenic gold deposits in the world class mana district of burkina faso revealed by la icp ms analysis of pyrites and arsenopyrites abstract mana is a world class paleoproterozoic orogenic gold district 8 0 moz that includes five gold deposits fofina nyafe siou wona kona and yaho hosted in various rocks in the northern part of the birimian hounde greenstone belt western burkina faso the gold deposits recorded different styles of mineralization associated with sulfides during polyphase deformation events detailed petrographic and la icp ms analyses of pyrites and arsenopyrites from the main mineralization of each deposit provide new information on the potential gold and arsenic sources and timing of fluids responsible for mineralization at mana four hydrothermal fluid events associated with two distinct source reservoirs and at least two hydrothermal systems were recognized the first hydrothermal fluid event was generated during the eoeburnean d1md md for mana district shortening event 2172 ma evidence of which is preserved in the fofina and siou deposits and occurred under greenschist metamorphic facies conditions economic gold deposits at fofina are associated with metamorphic disseminated pyrite py1f in black shale zoned pyrite py2f enriched in as ni cu ag sb w au and pb and arsenopyrite in folded v1f quartz carbonate veins in contrast the siou deposit exhibits au in porous pyrite cores py1s which are associated with ag bi te and w sb in v1s quartz veins hosted in the siou granodiorite these two trace element suites are interpreted as having been induced by a metamorphic source in the fofina deposit and by a local contribution of a magmatic source in the siou deposit the second hydrothermal fluid event occurred during the eburnean d3md transpressional event 2113 2090 ma in the nyafe deposit this event is defined by au as rich rims in hydrothermal pyrite py3n and by the co precipitation of au rich arsenopyrite in the v3n quartz veinlets v3n controlled by a second order dextral shear zone the third and main hydrothermal fluid event during the d4md transpressional event 2090 ma is characterized by the development of strong silicification and by zoned pyrites py3wk and py2y and au rich arsenopyrite in the wona kona and yaho deposits however the same late au as rich rims in hydrothermal pyrite are observed in both deposits and in the nyafe deposit and these rims are interpreted to be related to the same economic gold source related to the lower birimian metamorphic reservoir composed of black shale diagenetic framboidal pyrite and tholeiitic basalts the diagenetic framboidal py1wk in black shale lower birimian group is enriched in au median of 0 8 ppm low in as median of 70 ppm with other trace elements ni cu zn ag sb and pb the last hydrothermal event is associated with free gold remobilization in late microfractures in the wona kona and siou deposit during the reactivation of major transcurrent shear zones during the d4md event or the d5md shortening event as late as 2022 ma a binary diagram of as ag vs sb bi appears to be effective at separating the diagenetic magmatic and metamorphic pyrites and could be used in orogenic gold exploration to ascertain potential gold endowment at the district scale

the gounkoto au deposit west africa constraints on ore genesis and volatile sources from petrological fluid inclusion and stable isotope data the loulo gounkoto complex in the kedougou kenieba inlier hosts three multi million ounce orogenic gold deposits situated along the senegal mali shear zone this west malian gold belt represents the largest west african orogenic gold district outside ghana the gounkoto deposit is hosted to the south of the gara and yalea gold mines in the kofi series metasedimentary rocks the ore body is structurally controlled and is characterised by sodic and phyllic alteration as and fe rich ore assemblages with abundant magnetite and overall enrichment in fe as cu au ag w ni co ree minor te pb se cd fluid inclusion analysis indicates that the deposit formed at p t conditions of approximately 1 4 kbar and 340 c and that two end member fluids were involved in mineralisation 1 a moderate temperature 315 340 c low salinity 10 wt nacl equiv low density 1 g cm 3 h2o co2 nacl h2s n2 ch4 fluid 2 a high temperature up to 445 c hypersaline 40 wt nacl equiv high density 1 3 g cm 3 h2o co2 nacl fecl2 fluid partial mixing of these fluids within the jog zone at gounkoto enhanced phase separation in the aqueo carbonic fluid and acted as a precipitation mechanism for au these findings demonstrate the widespread if heterogeneously distributed nature of fluid mixing as an ore forming process in the loulo gounkoto complex operating over at least a 30 km strike length of the shear zone stable isotope analyses of ore components at gounkoto indicate a dominant metamorphic source for h2o h2s and co2 and by extension au it thus can be reasoned that both the aqueo carbonic and the hypersaline fluid at gounkoto are of metamorphic origin and that the high levels of salinity in the brine are likely derived from evaporite dissolution

metallogenesis of the paleoproterozoic piaba orogenic gold deposit sao luis cratonic fragment brazil piaba is an orogenic gold deposit 3 5 moz of the sao luis cratonic fragment in north northeastern brazil the deposit is epizonal mesozonal and associated with the development of a subvertical strike slip fault that cut across rhyacian metavolcano sedimentary rocks and granitoids the metavolcano sedimentary sequence comprises carbon bearing schists andesite dacite ultramafic rocks and felsic tuffs formed at 2240 5 ma to 2227 33 ma that were intruded at 2214 3 ma by fine grained subvolcanic granophyric granodiorite whole rock geochemistry indicates that the hosting metavolcano sedimentary sequence formed in a subduction related arc back arc setting which has previously been interpreted as the early arc stage of an accretionary orogen 2240 2214 ma that was followed by voluminous subduction related calc alkaline arc magmatism 2168 2145 ma and by a collisional phase 2100 15 ma that produced several bodies of peraluminous granites the hydrothermal alteration of the host rocks produced early distal carbonization and hematitization and proximal ore related chlorite sericite carbonate sulfide alteration two styles of mineralization occurring in association are present 1 a network of thin quartz sulfide veinlets and subordinate narrow breccia veins with refractory to free milling gold dissemination in hydrothermally altered host rocks and 2 subordinate low sulfide au quartz veins with free milling gold fluid inclusions and stable isotopes characterize the mineralizing solution as a relatively reduced log fo2 30 to 35 neutral to slightly alkaline ph 5 to 6 2 low salinity average 5 nacl aqueous carbonic xco2 5 to 59 mol xh2o 40 to 93 mol xn2 and xch4 1 mol metamorphic fluid 18oh2o 5 5 to 8 9 dh2o 8 to 69 and suggest that gold mineralization occurred at 250 to 330 c and 1 25 to 2 8 kbar in response to phase separation and fluid rock interactions that produced sulfidation and minor carbonatization sulfur 34s 2 7 to 3 8 is from an undetermined source probably magmatic oxidized or sedimentary lead isotope compositions of gold ore related pyrite and k feldspar from regional rocks suggest that collision related granitoids of ca 2100 15 ma are the most likely sources for pb in the ore although mantle and lower crustal sources are also observed 40ar 39ar in hydrothermal sericite yielded a plateau age of 1980 13 ma which is similar to the pb pb model age of gold of 1959 ma these are considered the minimum age for gold mineralization whereas the maximum age of 2009 11 ma is given by a small gold hosting intrusion in the same region

metabasalts as sources of metals in orogenic gold deposits although metabasaltic rocks have been suggested to be important source rocks for orogenic gold deposits the mobility of au and related elements as sb se and hg from these rocks during alteration and metamorphism is poorly constrained we investigate the effects of increasing metamorphic grade on the concentrations of au and related elements in a suite of metabasaltic rocks from the otago and alpine schists new zealand the metabasaltic rocks in the otago and alpine schists are of morb and wpb affinity and are interpreted to be fragments accreted from subducting oceanic crust gold concentrations are systematically lower in the higher metamorphic grade rocks average au concentrations vary little between sub greenschist 0 9 0 5 ppb and upper greenschist facies 1 0 0 5 ppb but decrease significantly in amphibolite facies samples 0 21 0 07 ppb the amount of au depleted from metabasaltic rocks during metamorphism is on a similar scale to that removed from metasedimentary rocks in otago arsenic concentrations increase with metamorphic grade with the metabasaltic rocks acting as a sink rather than a source of this element the concentrations of sb and hg decrease between sub greenschist and amphibolite facies but concentration in amphibolite facies rocks are similar to those in unaltered morb protoliths and therefore unaltered oceanic crust cannot be a net source of sb and hg in a metamorphic environment the concentrations of au as sb and hg in oceanic basalts that have become integrated into the metamorphic environment may be heavily influenced by the degree of seafloor alteration that occurred prior to metamorphism we suggest that metasedimentary rocks are much more suitable source rocks for fluids and metals in orogenic gold deposits than metabasaltic rocks as they show mobility during metamorphism of all elements commonly enriched in this style of deposit

the relationship between particle characteristics and frictional strength in basal fault breccias implications for fault rock evolution and rockslide susceptibility abstract microstructural analysis of fault rock breccias along the basal shear zone bsz of potential rock slope failures in norway demonstrates that particle size distribution curves show a spectrum from particle to matrix supported we demonstrate that variation in residual shear strength from 450 to 700 kpa is directly related to particle size and shape characteristics we also show that these characteristics are dependent on the fault rock evolution and breakdown mechanism and demonstrate this with simulated examples particle supported fault rocks have higher residual strength than matrix supported samples as the amount of fine material increases the residual shear strength of the fault material decreases particle aspect ratio is variable suggesting different comminution mechanisms and fault zone evolution as particle size decreases below 10 20 m particle aspect ratio approaches 1 1 suggesting that as the fault rock evolves the particles become rounder as aspect ratio increases fault strength decreases we contend that the susceptibility of potential rock slope failures is fundamentally linked to and depends partly on the microscopic properties of the underlying fault rocks and is linked to their comminution history

formation of gold deposits a metamorphic devolatilization model a metamorphic devolatilization model can explain the enrichment segregation timing distribution and character of many goldfields such as those found in archean greenstone belts slate belts and other gold only provinces in this genetic model hydrated and carbonated greenschist facies rocks particularly metabasic rocks are devolatilized primarily across the greenschist amphibolite facies boundary in an orogenic setting devolatilization operates on the scale of individual mineral grains extracting not just h2o and co2 but also s and in turn au elevated gold in solution is achieved by complexing with reduced s and by h2co3 weak acid buffering near the optimal fluid ph for gold solubility the buffering is more important than being at the point of maximum gold solubility low salinity ensures low base metal concentrations in the auriferous metamorphic fluid migration of this fluid upwards is via shear zones and or into hydraulic fracture zones in rocks of low tensile strength the geometry of the shear zones dictates the kilometre scale fluid migration paths and the degree of fluid focusing into small enough volumes to form economic accumulations of gold deposition of gold from solution necessitates breakdown of the gold thiosulphide complex and is especially facilitated by fluid reduction in contact with reduced carbon bearing host rocks and or by sulphidation of wallrocks to generate iron bearing sulphide and precipitated gold as such black slate carbon seams banded iron formation tholeiitic basalt magnetite bearing diorite and differentiated tholeiitic dolerite sills are some of the important hosts to major goldfields gold deposition is accompanied by carbonation sulphidation and muscovite biotite alteration where the host rock is of suitable bulk composition the correlation of major gold deposits with rock type even when the gold is primarily in veins argues for rock dominated depositional systems not fluid dominated ones as a consequence a general role in gold deposition for fluid mixing temperature decrease and or fluid pressure decrease and boiling is unlikely although such effects may be involved locally several geological features that are recorded at gold only deposits today reflect subsequent modifications superimposed upon the products of this generic metamorphic devolatilization process overprinting by higher grade metamorphism and deformation and or palaeo weathering may provide many of the most obvious features of goldfields including their mineralogy geochemistry geometry small scale timing features geophysical response and even mesoscopic gold distribution

ultrasonic velocity and anisotropy of hydrocarbon source rocks an experimental study of the physical properties of black kerogen rich shales also including maturation analysis scanning electron microscope sem observations and physical modeling revealed fairly peculiar petrophysical parameters specifically these rocks have very low porosity and density but most importantly both p and s ultrasonic velocities normal to bedding are extremely low whereas they are much higher parallel to bedding giving rise to a strong anisotropy even at high confining pressures we found that these parameters primarily reflect kerogen content microstructure and maturation level of these rocks we found also that microcracks inferred from ultrasonic velocity measurements occur only in mature shales these microcracks are parallel to the bedding plane and further enhance strong intrinsic anisotropy notably at low effective pressure our results show that on a small scale kerogen rich shales are transversely isotropic rocks and can be effectively modeled using the thin laye

ring shear studies of till deformation coulomb plastic behavior and distributed strain in glacier beds a ring shear device was used to study the factors that control the ultimate steady strength of till at high shear strains tests at a steady strain rate and at different stresses normal to the shearing direction yielded ultimate friction angles of 26 3 and 18 6 for tills containing 4 and 30 clay sized particles respectively other tests at steady normal stresses and variable shear strain rates indicated a tendency for both tills to weaken slightly with increasing strain rate this weakening may be due to small increases in till porosity these results provide no evidence of viscous behavior and suggest that a coulomb plastic idealization is reasonable for till deformation however viscous behavior has often been suggested on the basis of distributed shear strain observed in subglacial till we hypothesize that deformation may become distributed in till that is deformed cyclically in response to fluctuations in basal water pressure during a deformation event transient dilation ofdiscrete shear zones should cause a reduction in internal pore water pressure that should strengthen these zones relative to the surrounding till a process called dilatant hardening consequent changes in shear zone position when integrated over time may yield the observed distributed strain

consistency of stress state locations and source mechanisms of events induced by hydraulic fracturing downhole monitoring we present results of processed microseismic events induced by hydraulic fracturing and detected using dual downhole monitoring arrays the results provide valuable insight into hydraulic fracturing for our study we detected and located microseismic events and determined their magnitudes source mechanisms and inverted stress field orientation event locations formed a distinct linear trend above the stimulated intervals source mechanisms were only computed for high quality events detected on a sufficient number of receivers all the detected source mechanisms were dip slip mechanisms with steep and nearly horizontal nodal planes the source mechanisms represented shear events and the non double couple components were very small such small non double couple components are consistent with a noise level in the data and velocity model uncertainties strikes of inverted mechanisms corresponding to the nearly vertical fault plane are within the error of measurements identical with the strike of the location trend ambient principal stress directions were inverted from the source mechanisms the least principal stress 3 was determined perpendicular to the strike of the trend of the locations indicating that the hydraulic fracture propagated in the direction of maximum horizontal stress our analysis indicated that the source mechanisms observed using downhole instruments are consistent with the source mechanisms observed in microseismic monitoring arrays in other locations furthermore the orientation of the inverted principal components of the ambient stress field is in agreement with the orientation of the known regional stress implying that microseismic events induced by hydraulic fracturing are controlled by the regional stress field

geochemistry of shale and sedimentary pyrite as a proxy for gold fertility in the selwyn basin area yukon selwyn basin area strata contain sedimentary pyrite with au above background levels when analyzed by laser ablation inductively coupled mass spectrometry hyland group rocks contain framboidal pyrite contents of 670 ppb au 1223 ppm as and 5 3 ppm te the mean of all types of sedimentary pyrite in the hyland group is 391 ppb au 1489 ppm as and 3 8 ppm te these levels are similar to sedimentary pyrite in host lithologies from major orogenic gold districts in new zealand and australia comparison of whole rock and pyrite data show that rocks deposited in continental slope settings with significant terrigenous input contain pyrite that is consistently enriched in au as te co and cu although data are limited whole rock samples of stratigraphic units containing au rich pyrite also contain high au indicating that most of the au is within sedimentary pyrite based on geologic characteristics and comparison of pyrite chemistry data with whole rock chemistry selwyn basin area strata have the necessary ingredients to form orogenic gold deposits au enriched source rocks metamorphic conditions permissive of forming a metamorphic ore fluid and abundant structural preparation for channeling fluids and depositing ore

geochemistry of reduced gas related to serpentinization of the zambales ophiolite philippines abstract methane hydrogen gas seeps with mantle like c and noble gas isotopic characteristics issue from partially serpentinized ultramafic rocks in the zambales ophiolite philippines new measurements of noble gas and 14c isotope abundances rock mixed volatile equilibrium calculations and previous chemical and isotopic data suggest that these reduced gases are products of periodotite hydration the gas seeps are produced in rock dominated zones of serpentinization and similar gases may be ubiquitous in ultramafic terranes undergoing serpentinization

full waveform based complete moment tensor inversion and source parameter estimation from downhole microseismic data for hydrofracture monitoring downhole microseismic monitoring is a valuable tool in understanding the efficacy of hydraulic fracturing inverting for the moment tensor has gained increasing popularity in recent years as a way to understand the fracturing process previous studies utilize only part of the information in the waveforms such as direct p and s wave amplitudes and make far field assumptions to determine the source mechanisms the method is hindered in downhole monitoring when only limited azimuthal coverage is available in this study we develop an approach to invert for complete moment tensor using full waveform data recorded at a vertical borehole we use the discrete wavenumber integration method to calculate full wavefields in the layered medium by using synthetic data we find that at the near field range a stable complete moment tensor can be retrieved by matching the waveforms without additional constraints at the far field range we discover that the off plane moment tensor component is poorly constrained

fluid signature of the shear zone controlled veio de quartzo ore body in the world class bif hosted cuiaba gold deposit archaean rio das velhas greenstone belt brazil a fluid inclusion study the world class cuiaba gold deposit of the archaean rio das velhas greenstone belt in brazil is hosted in banded iron formation containing carbonaceous matter and carbonate within the reclined isoclinal cuiaba fold mineralised quartz veins are hosted in andesite in the stratigraphic footwall of the banded iron ores and form some of the more recently discovered ore bodies fluid inclusion data of the quartz vein associated veio de quartzo ore body are obtained from four quartz types qz1 qz2 qz3 qz5 in gold mineralised v1 shear vein and v2 extensional veins barren v3 extensional vein array and v4 breccia style veins all developed during the archaean d1 event three fluid types are distinguished i aqueous fluids of low salinity 1 8 3 8 wt nacl equiv homogenisation into liquid at 220 to 230 c ii aqueous fluids of moderate salinity 5 3 12 7 wt nacl equiv and homogenisation at 250 to 290 c and iii aqueous carbonic fluids of moderate salinity 6 0 15 1 wt nacl equiv with 30 91 mol co2 8 41 mol ch4 and up to 28 mol n2 and decrepitation into vapour at 280 to 310 c based on an independent pressure estimate a pressure correction was applied to aqueous fluid inclusions resulting in minimum trapping temperatures at 360 c for v1 veins 330 c for v2 veins 300 c for v3 veins and 270 c for the late stage v4 veins ion chromatography analyses reveal a br cl ratio of 0 7 10 3 in qz1 v1 from 1 4 to 1 5 10 3 in qz2 v2 0 3 to 0 4 10 3 in qz3 v3 and 0 7 to 0 9 10 3in qz5 v4 veins zinc pb and cu are relatively enriched with 100 to 1000 ppm in aqueous and aqueous carbonic fluid inclusion assemblages in all vein and quartz types which is similar to other orogenic gold deposits hosted in the rio das velhas greenstone belt the fluid inclusion data are consistent with a model invoking a metamorphic origin for the mineralising fluid a two step model of hydrothermal fluid flow and gold enrichment is suggested to have developed during the archaean d1 event with an early aqueous carbonic fluid pulse of relatively high temperature from v1 up to v3 and an evolved aqueous carbonic fluid pulse of lower temperature v4 breccia style veins the rio das velhas greenstone belt is dominated by regionally metamorphosed metasedimentary rocks resulting in a complex hydrothermal fluid evolution and related gold mineralisation such as the shear zone controlled veio de quartzo ore body

development of deep seated gravitational slope deformation on a shale dip slope observations from high quality drill cores abstract we analyzed high quality drill cores with 100 recovery drilled into a gravitationally deformed dip slope of a shale dominated sequence of sediments in japan the slope had undulating surfaces but no well defined landslide scarps suggesting that parts of the slope had undergone gravitational deformation but had not completely separated from the surrounding bedrock the gravitational deformation of shale and sandstone is characterized by disintegration and brecciation of sediments and the formation of pulverized zones with poorly developed planar structures jigsaw like structures and fracture openings shear zones are distributed intermittently within the slope but have not merged discernably into a through going master sliding surface incipient landslide shear zones form openings within coherent rock by shearing along bedding with these shear zones potentially developing downward in a stepwise manner which may be related to stress redistribution induced by river incision

paragenesis and composition of ore minerals in the randalls bif hosted gold deposits yilgarn craton western australia implications for the timing of deposit formation and constraints on gold sources the randalls district comprises three individual gold deposits cock eyed bob maxwells and santa craze hosted in the same unit of banded iron formation bif in the southern eastern goldfields superterrane yilgarn craton western australia the iron formation is a silicate oxide facies unit with overprinting sulfides and has undergone metamorphism upper greenschist facies and deformation two generations of folds the gold deposits are hosted in two structural locations hinge zones of anticlinal folds e g santa craze and maxwells and overturned steeply dipping limbs of anticlinal folds e g cock eyed bob gold dominantly occurs as inclusions of native gold and or electrum within or around pyrrhotite magnetite and arsenopyrite the earliest mineral assemblage preserved in the banded iron formation at randalls is banded magnetite quartz magnetite in all forms has elevated mg al ti v mn cr zn and w but very low ni compared to other bifs globally pyrrhotite the most abundant sulfide is restricted to ore zones and occurs as laminae blebs and veinlets all of which have replaced magnetite some pyrrhotite in the hydrothermally altered bifs especially in near surface samples has been re sulfidized to pyrite trace elements associated with pyrrhotite include co ni ag sb and pb large coarse grained arsenopyrite overgrows the pyrrhotite defined foliation it is enriched in co ni sb and te but contains very little invisible gold 0 01 ppm au unlike arsenopyrite in many orogenic au systems globally commonly 0 1 ppm au petrographic studies of several mineralized bifs from randalls reveal that pyrrhotite and arsenopyrite are associated with fe ca amphibole which grew during contact metamorphism caused by granite plutons this spatial sulfide amphibole relationship indicates that gold mineralization likely occurred during granite intrusion consistent with prior studies on randalls the trace element characteristics of the sulfides show that they were not inherited from replaced magnetite further these characteristics suggest that the fluid from which sulfides crystallized was not indigenous to the bifs and that this s rich fluid either contained s in abundance originally or interacted with a lithology lithologies that were rich in s before reaching the bifs black shale containing diagenetic nodular pyrite occurs in the upper black flag group which unconformably underlies the belches supersequence at depth 3 km the trace element composition of nodular pyrite from this unit fits well with the trace element characteristics of the bif pyrrhotite and arsenopyrite and the nodular pyrite contains an average of 0 5 ppm au however the nodular pyrites have an average 34s value of 5 6 n 13 which contrasts markedly with the 34s average of pyrrhotite pyrite and arsenopyrite in mineralized bifs 0 8 n 17 thus a definitive source of gold arsenic silver and tellurium in the randalls system remains elusive although we would contend that the upper black flag group should be considered as a possible metal and s source in areas of the yilgarn where it forms a thick substrate to ore camps

a carbonaceous sedimentary source rock model for carlin type and orogenic gold deposits this paper presents evidence and arguments that carbonaceous sedimentary rocks were a source for au and as in sediment hosted orogenic and carlin type gold deposits and develops a corresponding genetic model in this two stage basin scale model gold and arsenic are introduced early into black shale and turbidite basins during sedimentation and diagenesis stage 1 and concentrated to ore grades by later hydrothermal structural or magmatic processes stage 2 in reduced continental margin basin settings organic matter sedimented under anoxic to euxinic conditions immobilizes and concentrates gold arsenic and a range of trace elements particularly v ni se ag zn mo cu u present in marine bottom waters into fine grained black mudstone and siltstone of slope and basin facies during early diagenesis gold and certain other trace elements ni se te ag mo cu pge are preferentially partitioned into arsenian pyrite that grows in the muds these processes produce regionally extensive black shale and turbidite sequences enriched in syngenetic gold and arsenic commonly from 5 to 100 ppb au and 10 to 200 ppm as rare organic and sulfide rich metalliferous black shales may contain up to 1 to 2 ppm au and over 1 000 ppm as present as refractory gold in arsenian pyrite and nanoparticles of free gold during late diagenesis and early metamorphism stage 2 the diagenetic arsenian pyrite is recrystallized to form coarser grained pyrite generations and the organic matter is cooked to bitumen under higher grade metamorphism lower greenschist facies and above arsenian pyrite in carbonaceous shales is converted to pyrrhotite these processes release gold arsenic sulfur and other elements sb te cu zn mo bi tl and pb from the source rocks to become concentrated by hydrothermal processes locally to produce gold ores in structural sites such as fold hinge zones shear or breccia zones within or above the black shale sequence la icp ms analyses of diagenetic pyrite in carbonaceous sediments both associated and not associated with gold deposits suggests that invisible gold contents of greater than 250 ppb in diagenetic pyrite are indicative of carbonaceous shale source rocks with the potential to produce economic gold deposits application of this sedimentary source rock model enables a systematic exploration approach for sediment hosted gold deposits based on the distribution composition and structure of carbonaceous shale sequences and their contained diagenetic pyrite

tectonic framework for late cretaceous to eocene quartz gold vein mineralization from the caborca orogenic gold belt in northwestern mexico

a 2d and 3d nanostructural study of naturally deformed pyrite assessing the links between trace element mobility and defect structures the links between deformation induced micro and nanostructures and trace element mobility in sulphide minerals have recently become a popular subject of research in the earth sciences due to its connections with metallic ore paragenesis it has been shown that plastic deformation in pyrite creates diffusion pathways in the form of low angle grain boundaries that act as traps for base and precious metals however the plastic behavior of pyrite and the physiochemical processes that concentrate these trace elements in deformation induced micro and nanostructures remain poorly understood in this study we develop strategies for 2d and 3d analysis of naturally deformed sulphides by combining electron backscatter diffraction electron channeling contrast imaging and atom probe tomography on pyrite in an attempt to better understand the underlying diffusion processes that mobilize trace elements the combined results reveal structures associated with crystal plastic deformation in the form of dislocations stacking faults and low angle grain boundaries that are decorated by as and co although our data support a dislocation impurity pair diffusion model we have evidence that multiple diffusion mechanisms may have acted simultaneously in this study we applied new data processing techniques that allow for orientation measurement of nanostructural crystal defects from atom probe tomography data dislocations within our studied sample occur along the 110 planes suggesting glide on 110

giant rockslides from the inside the growing body of research on large scale mass wasting events so far has only scarcely investigated the sedimentology of chaotic deposits from non volcanic terrestrial landslides such that any overarching and systematic terminological framework remains elusive yet recent work has emphasized the need for better understanding the internal structure and composition of rockslide deposits as a means to characterise the mechanics during the final stages of runout and emplacement we offer a comprehensive overview on the occurrence of rock fragmentation and frictional melt both at different geographic locations and different sections within large 10 6 m 3 rockslide masses we argue that exposures of pervasively fragmented and interlocked jigsaw cracked rock masses basal melange containing rip up clasts and phantom blocks micro breccia and thin bands of basal frictionite are indispensable clues for identifying deposits from giant rockslides that may remain morphologically inconspicuous otherwise these sedimentary assemblages are diagnostic tools for distinguishing large rockslide debris from macro and microscopically similar glacial deposits tectonic fault zone breccias and impact breccias and thus help avoid palaeoclimatic and tectonic misinterpretations let alone misestimates of the hazard from giant rockslides moreover experimental results from mossbauer spectroscopy of frictionite samples support visual interpretations of thin sections and demonstrate that short lived 1500 degrees c in the absence of water occurred at the base of several giant moving rockslides this finding supports previous theories of dry excess runout accompanied by comminution of rock masses down to gm scale and indicates that catastrophic motion of large fragmenting rock masses does not require water as a potential lubricant

full waveform based microseismic source mechanism studies in the barnett shale linking microseismicity to reservoir geomechanics abstractseismic moment tensors mts of microearthquakes contain important information on the reservoir and fracturing mechanisms difficulties arise when attempting to retrieve complete mt with conventional amplitude inversion methods if only one well is available with the full waveform approach near field information and nondirect waves i e refracted reflected waves help stabilize the inversion and retrieve complete mt from the single well data set however for events which are at far field from the monitoring well a multiple well data set is required in this study we perform the inversion with a dual array data set from a hydrofracture stimulation in the barnett shale determining source mechanisms from the inverted mts requires the use of a source model which in this case is the tensile earthquake model the source information derived includes the fault plane solution slip direction vp vs ratio in the focal area and seismic moment the primary challenge of extracting source parameters fro

moment tensor inversion of microseisms from the b sand propped hydrofracture m site colorado abstract we apply a moment tensor inversion algorithm to microseismic events generated by hydrofracturing our dataset consists of microseismic events associated with a hydraulic fracturing experiment conducted at the gri doe m site near rifle colorado the event recordings were from a vertical string of 3 component accelerometer pods that are cemented in a borehole the accelerograms clearly show p and s waves which can be rotated into the sh and sv components to invert the p and s amplitudes for moment tensors we use just the first two peaks after the first arrival using this amplitude information and the average pulse width we formed a symmetric stylized pulse for integration and we inverted for the moment tensor resolution tests revealed that with the source microseism to receiver geometry we have at the m site where all receivers are in one borehole and at the same azimuth from the source we can extract the five deviatoric components of the moment tensor using combinations of p sh and sv amplitudes for example a minimum data set of 3 p wave 2 sv wave and 1 sh wave amplitudes to obtain the sixth component which is the isotropic component requires amplitude information from receivers at another azimuth we studied seven high quality events in detail and tested their results against two alternative source geometries these microseismic events tend to have a major double couple nodal plane aligned parallel to the main hydrofracture plane rather than have their tension t axes aligned parallel to the regional minimum principal compressive stress direction the events have seismic moments m0 on the order of 10 5 nm and moment magnitudes mw of about 2 5

pyrite and pyrrhotite textures and composition in sediments laminated quartz veins and reefs at bendigo gold mine australia insights for ore genesis the various types textures and compositional zoning of pyrite in the gold bearing saddle reefs quartz veins and surrounding sedimentary rocks provide new information on the potential source and timing of gold and arsenic and related fluid processes responsible for mineralization at bendigo nodular diagenetic pyrite in the black shale tops to sandstone turbidites is enriched in invisible gold and arsenic with mean values of 0 61 ppm au 1 300 ppm as and au ag 1 based on la icpms analyses other elements enriched in the diagenetic pyrite within the organic rich shales are mn zn mo cu v ba ag cd tl co ni bi pb and te in contrast euhedral and growth zoned hydrothermal pyrite in the turbidites and bedding parallel laminated quartz veins contains lower contents of most trace elements but has higher contents of invisible au and as especially on the outermost rim of the pyrite the gold rich pyrite rims generally become thicker a few to hundreds of microns in proximity to the gold bearing saddle reefs pyrite in the reef commonly has the highest levels of invisible au and as and the lowest levels of other trace elements it is characterized by au ag 1 and au pb 0 01 in the deepest stratigraphic levels below known productive gold reefs diagenetic pyrite in the most carbonaceous shales has been replaced by pyrrhotite during metamorphism la icpms analyses reveal that the disseminated pyrrhotite contains similar levels of ni and co to the diagenetic pyrite but is strongly depleted in as and au the spatial relationships between organic rich shales folded bedding parallel laminated quartz veins and gold arsenic bearing saddle reefs combined with the consistent trends in the trace element composition of pyrite hosted by these three geological elements is interpreted to indicate that the black shales were an initial source of au and as and the laminated quartz veins acted as the initial pathways for hydrothermal fluid flow carrying au and as from the source shales to the saddle reefs maximum gold and arsenic input into the reefs principally as free gold plus arsenopyrite occurred late during deformation toward the end of the hydrothermal cycle and is expressed by the au as rich rims to hydrothermal pyrite in the sedimentary host rocks laminated quartz veins and reefs this corresponds with final fold lockup and the development of through going fault arrays linking adjacent anticlines the source of au and as for this final and most economically important fluid flow event is considered to be from carbonaceous shales deeper in the basin where original gold bearing diagenetic arsenian pyrite reacts with organic matter and is converted to pyrrhotite with release of au as and s to the metamorphic fluid

on the retrieval of moment tensors from borehole data the complete moment tensors of seismic sources in homogeneous or vertically inhomogeneous isotropic structures cannot be retrieved using receivers deployed in one vertical borehole the complete moment tensors can be retrieved from amplitudes of p waves provided that receivers are deployed in at least three boreholes using amplitudes of p and s waves two boreholes are in principle sufficient similar rules also apply to transversely isotropic media with a vertical axis of symmetry in the case of limited observations the inversion can be stabilized by imposing the zero trace constraint on the moment tensors however this constraint is valid only if applied to observations of shear faulting on planar faults in isotropic media which produces double couple mechanisms for shear faulting on non planar faults for tensile faulting and for shear faulting in anisotropic media the zero trace constraint is no longer valid and can distort the retrieved moment tensor and bias the fault plane solution numerical modelling simulating the inversion of the double couple mechanism from real data reveals that the errors in the double couple and non double couple percentages of the moment tensors rapidly decrease with increase in the number of boreholes used for noisy p and s wave amplitudes with noise of 15 of the top amplitude at each channel and for a velocity model biased by 10 the errors in the double couple percentage attain 25 13 and 6 when inverting for the double couple mechanism from one two and three boreholes

fault related rocks suggestions for terminology many traditional terms for fault related rocks have undergone recent dynamic metamorphism under high pressure discussions by various groups of specialists a generally acceptable simplified framework encompassing these and associated structural terms is now needed for many geologic engineering and legal purposes such a framework is proposed here focusing on a rate of strain versus rate of recovery diagram and relating this framework to the products of brittle and ductile deformation along faults

orogenic gold common or evolving fluid and metal sources through time abstract orogenic gold deposits of all ages from paleoarchean to tertiary show consistency in chemical composition they are the products of aqueous carbonic fluids with typically 5 20 mol co 2 although unmixing during extreme pressure fluctuation can lead to entrapment of much more co 2 rich fluid inclusions in some cases ore fluids are typically characterized by significant concentrations of ch 4 and or n 2 common estimates of 0 01 0 36 mol h 2 s a near neutral ph of 5 5 and salinities of 3 7 wt nacl equiv with na k ca mg this fluid composition consistency favors an ore fluid produced from a single source area and rules out mixing of fluids from multiple sources as significant in orogenic gold formation nevertheless there are broad ranges in more robust fluid inclusion trapping temperatures and pressures between deposits that support a model where this specific fluid may deposit ore over a broad window of upper to middle crustal depths much of the reported isotopic and noble gas data is inconsistent between deposits leading to the common equivocal interpretations from studies that have attempted to define fluid and metal source areas for various orogenic gold provinces fluid stable isotope values are commonly characterized by the following ranges 1 18 o for precambrian ores of 6 to 11 and for phanerozoic ores of 7 to 13 2 d and 34 s values that are extremely variable 3 13 c values that range from 11 to 2 and 4 15 n of 10 to 24 for the neoarchean 6 5 to 12 for the paleoproterozoic and 1 5 to 10 for the phanerozoic secular variations in large scale earth processes appear to best explain some of the broad ranges in the o s and n data fluid rock interaction particularly in ore trap areas may cause important local shifts in the o s and c ratios the extreme variations in d mainly reflect measurements of hydrogen isotopes by bulk extraction of waters from numerous fluid inclusion generations many which are not related to ore formation radiogenic isotopes such as those of pb sr nd sm and os measured on hydrothermal minerals are even more difficult to interpret for defining metal source particularly as the low salinity ore fluids transport limited amounts of these elements and significant amounts of these may be locally added to the minerals during alteration reactions at the sites of gold deposition noble gas and halogen data are equally equivocal fluid exsolution from granitoids emplaced into the upper and middle crust metamorphism of the crust or fluids entering trans crustal fault zones from below the crust all remain as permissive scenarios associated with orogenic gold formation as the abundant geochemical data are equivocal however geological and geochronological data weigh heavily against a magmatic hydrothermal model in the upper to middle crust there is no universal temporal association between orogenic gold and magmatism and where there is an overlap in age there is no specific type of magmatism consistently associated with gold formation nor element zonation around any specific pluton a crustal metamorphic model for fluid and metal sources is very consistent with geological geochronological and geochemical data although metamorphism on a regional scale that releases these components into major fault zones can be associated with many processes along active continental margins these can include crustal thickening and radiogenic heating slab rollback and heating during crustal extension or subduction of a spreading ridge heating the base of an accretionary prism in rare examples where phanerozoic orogenic gold deposits are hosted in precambrian high grade metamorphic terranes fluids and metals must however enter a transcrustal fault system from a sub crustal source this could either be a devolatilized subducted relatively flat perhaps stalled slab and its overlying sediment or the corner of the fertilized mantle wedge that releases a fluid during a thermal event

fluid inclusions in quartz pebbles of the gold bearing tarkwaian conglomerates of ghana as guides to their provenance area quartz pebbles of the early proterozoic au bearing tarkwaian conglomerates in ghana reveal several original inherited pre sedimentary fluid inclusions these inclusions are co2 n2 rich and display a distinct high density up to 1 15 g cm3 the unusual high density and composition compare well with co2 n2 rich inclusions in quartz vein type gold deposits of the birimian supergroup in ghana and burkina faso this type of fluid inclusions has not been reported from any other lode gold deposit of greenstone affiliation and is thus a specific characteristic for birimian hosted gold deposits therefore it can be used as an unequivocal pathfinder for epigenetic as well as for syn sedimentary gold mineralization of the early proterozoic of west africa the inherited fluid inclusions with the unique physicochemical characteristics suggest that the tarkwaian quartz pebbles and possibly some gold were derived from au quartz vein deposits comparable in mineralogy petrography and genesis to those along the nw margin of the ashanti belt e g ashanti mine prestea mine

the genesis of gold mineralisation hosted by orogenic belts a lead isotope investigation of irish gold deposits abstract lead isotope analyses have been performed on 109 gold and 23 sulphide samples from 34 irish gold occurrences including 27 placers and used to shed light on the sources of mineralising fluids and metals associated with gold mineralisation hosted by orogenic belts the pb isotope ratios of lode and placer gold range from 206pb 204pb 17 287 18 679 207pb 204pb 15 382 15 661 and 208pb 204pb 37 517 38 635 consistent with the pb isotopic data on previously reported irish sulphide mineralisation there is no evidence that gold mineralisation is associated with distinctive source regions and it appears to have been derived from similar sources to those responsible for the widespread sulphide mineralisation in ireland it is inferred that the principal controls on the au mineralisation are structural and not related to the distribution of au in their source rocks the range of pb isotope ratios favours the interaction of multiple source reservoirs predominantly during the caledonian orogeny c 475 380 ma underlying basement was the primary control on two key sources of pb gold occurrences located to the south east of the iapetus suture are characterised by pb compositions that derive predominantly from the late proterozoic crustal basement or overlying lower palaeozoic sediments whilst those located north west of the iapetus suture are characterised by less radiogenic pb signatures derived predominantly from late proterozoic or older crustal basement a third source relatively enriched in radiogenic pb also played a role in the formation of a number of irish gold occurrences and may have been associated with syn to post orogenic intrusives magmatic processes may therefore have played an important role in the formation of some orogenic gold occurrences

constraints of fluid inclusions and in situ s pb isotopic compositions on the origin of the north kostobe sediment hosted gold deposit eastern kazakhstan abstract the north kostobe gold deposit in the kalba gold province eastern kazakhstan is tectonically located in the chara shear zone of the western altaids the chara shear zone separates the kazakhstan microcontinent and siberia craton which collided in the late carboniferous in the north kostobe deposit au mineralization is distributed along an e w striking shear zone linked to the nw se trending regional faults and is mainly concentrated in quartz sulfide carbonate veins or in disseminated sulfides hosted in carbonaceous metasedimentary rocks sulfide minerals are mainly pyrite and arsenopyrite and were formed in three generations the first generation is dominated by pyrite py1 occurring as microcrystal aggregates followed by the second generation including euhedral arsenopyrite and compact pyrite py2 locally overgrowing early py1 grains as rims third generation of pyrite py3 is present in barren micro fractures crosscutting early mineralized rocks native gold is present in cracks of brecciated arsenopyrite grains and as inclusions in py2 investigations on fluid inclusions in auriferous quartz veins indicate that the ore related fluids are co 2 bearing with homogenization temperatures of 288 c and low salinity 1 42 to 8 03 wt nacl equiv the fluids have calculated 18 o and d values ranging from 9 96 to 11 86 and from 75 to 97 1 respectively suggesting that they were most likely metamorphic in origin the first and second generations of ore sulfides have similar 34 s values 6 to 2 6 which possibly indicating a common sulfur source as the hosting sedimentary rocks in contrast py3 grains have a huge range of 34 s values 40 to 54 5 indicating a biogenic source for the sulfur on the other hand in situ pb isotopic compositions of different generations of sulfides show a similarly mixed lead source possibly involved orogen mantle and lower crust pb reservoirs we propose that the gold bearing fluids of the north kostobe gold deposit were most likely derived from gold rich pyritic carbonaceous sedimentary rocks through dehydration during the metamorphism that was related to the collision between the kazakhstan microcontinent and siberia craton in the late carboniferous it is thus concluded that the north kostobe gold deposit shares many characteristics with typical orogenic gold deposits in terms of tectonic settings mineralization styles fluid compositions and source of fluids and gold our new findings thus have important implications for regional exploration in the kalba gold province

geochemical origin of hydrothermal fluid methane in sediment associated fields and its relevance to the geographical distribution of whole hydrothermal circulation abstract we investigated the chemical composition of hydrothermal fluids and deduced the origin of hydrothermal fluid methane in a sediment associated minami ensei me hydrothermal field the okinawa trough the endmember hydrothermal fluid of the me field contained isotopically 13 c enriched methane 26 0 to 24 7 which suggested a thermogenic origin however the observed methane dominating hydrocarbon compositions c 1 c 2 10 3 suggested that biogenic methane not thermogenic hydrocarbons is predominant the conflict between these geochemical indications can be resolved by the hypothesis that the thermal reaction of sedimentary organic matter initially generates the primary source of hydrocarbons and the secondary thermal decomposition of hydrocarbons increases the c 1 c 2 ratio as high as that of biogenic methane the low molecular hydrogen concentration 0 04 mmol kg in the me fluid suggests that the thermal fluid sediment interaction occurred in the recharge stage not the discharge stage of hydrothermal circulation less biogenic methane in the me fluid implies a laterally shrunken hydrothermal fluid circulation that reduced biogenic methane incorporation at the recharge stage a comparison of hydrothermal fluid chemistry and geological geographical settings among the global sediment associated hydrothermal systems also suggests representative patterns in the geochemical origins of hydrothermal fluid methane and their relevance to hydrothermal fluid circulation as a whole

different carbon reservoirs of auriferous fluids in african archean and proterozoic gold deposits constraints from stable carbon isotopic compositions of quartz hosted co 2 rich fluid inclusions stable carbon and when present nitrogen isotope ratios of fluid inclusions in quartz from selected gold deposits in ghana and zimbabwe have been analyzed using a crushing device interfaced to an isotopic ratio mass spectrometer irms in order to constrain possible sources of the auriferous fluids the study revealed a striking difference in stable carbon isotopic compositions of co2 in quartz hosted fluid inclusions from archean and paleoproterozoic orogenic gold deposits and points to diverse sources of co2 in the studied deposits whether this finding can be generalized for other archean and proterozoic orogenic gold deposits worldwide remains open however a significant co2 contribution by mantle degassing can be ruled out for every deposit studied devolatilization of greenstone belt rocks is the most likely source for co2 in some archean au deposits in zimbabwe whereas co2 in proterozoic vein type au deposits in the west african craton is most likely derived from corg bearing metasedimentary rocks the 13cco2 values of high density co2 rich water poor inclusions hosted in quartz pebbles from the world class au bearing conglomerate deposits at tarkwa ghana differ considerably from the 13cco2 values of similar high density co2 rich inclusions in vein quartz from the giant ashanti deposit ghana and disprove the idea of derivation of the tarkwaian quartz and gold from an older equivalent to the ashanti vein type gold deposit

azimuthal anisotropy in microseismic monitoring a bakken case study abstracthydraulic fracturing routinely applied for enhancing the permeability of unconventional oil and gas reservoirs is one of the possible causes for azimuthal anisotropy of the treated formations accounting for both naturally occurring and completion induced azimuthal anisotropy leads to marked improvements in the results of microseismic data processing as illustrated on a data set acquired in the bakken field north dakota usa those improvements include the possibility of modeling the observed shear wave splitting reduction of misfit between the picked and modeled traveltimes of microseismic events and relocation and tightening of the spatial distribution of the event hypocenters in addition and perhaps most importantly for the development of microseismic technology the feasibility of joint inversion of field microseismic data for the event locations and azimuthally anisotropic velocity model containing triclinic layers is demonstrated

ore deposits in an evolving earth an introduction ore deposits form by a variety of natural processes that concentrate elements into a small volume that can be economically mined their type character and abundance reflect the environment in which they formed and thus they preserve key evidence for the evolution of magmatic and tectonic processes the state of the atmosphere and hydrosphere and the evolution of life over geological time this volume presents 13 papers on topical subjects in ore deposit research viewed in the context of earth evolution these diverse yet interlinked papers cover topics including controls on the temporal and spatial distribution of ore deposits the sources of fluid gold and other components in orogenic gold deposits the degree of oxygenation in the neoproterozoic ocean bacterial immobilization of gold in the semi arid near surface environment and mineral resources for the future including issues of resource estimation sustainability of supply and the criticality of certain elements to society

influence of structural setting on sulphur isotopes in archean orogenic gold deposits eastern goldfields province yilgarn western australia the published mean 34s values of ore related pyrites from orogenic gold deposits of the eastern goldfields province yilgarn craton lie between 4 and 4 as for orogenic gold deposits worldwide most deposits have positive means and a restricted range of 34s values but some have negative means and wider ranges of 34s values wall rock carbonation and back mixing of similar source fluids with different fluid pathways can explain some of the more negative 34s signatures however structural setting appears to be the most important factor controlling ore fluid oxidation state and hence the distribution of 34s values in gold related pyrites shear hosted deposits appear to have experienced fluid dominated processes such as phase separation whereas stockwork vein hosted or disseminated deposits formed under conditions of greater rock buffering at victory defiance in particular negative 34s values are more common in gently dipping dilational structures compared to more compressional steeply dipping structures it appears most likely that fluid pressure fluctuations during fault valve cycles establish different fluid flow regimes in structures with different orientations rapid fluid pressure fluctuations in dilational structures during seismic activity can cause partitioning of reduced gas phases from the ore fluid during extreme phase separation and hence are an effective method of ore fluid oxidation leading to large local fluctuations in oxidation state it is thus not necessary to invoke mixing with oxidised magmatic fluids to explain 34s signatures indicative of oxidation in any case available robust geochronology in the eastern goldfields province does not support the direct involvement of oxidised magmatic fluids from adjacent granitic intrusions in orogenic gold genesis thus negative mean 34s values and large variations in 34s values of ore related pyrites in world class orogenic gold deposits are interpreted to result from multiple mechanisms of gold precipitation from a single ubiquitous ore fluid in varying structural settings rather than from the involvement of oxidised ore fluids from a different source such signatures are indicative but not diagnostic of anomalously large orogenic gold systems

the world class wona kona gold deposit burkina faso abstract the world class 4 moz wona kona gold deposit is hosted within the paleoproterozoic birimian hounde greenstone belt which is the most important gold mineralized belt in the western part of burkina faso with a cumulative reserve of 11 moz the mineralization consists of a pervasive silicification with disseminated pyrite arsenopyrite crosscut by quartz carbonate veinlets 1 to 10 cm wide forming a vertical thick up to 40 m and laterally extensive 5 km northeast trending orebody hosted within a large 200 m wide shear zone of regional extent gold occurs in association with 3 generations of pyrite and 2 generations of arsenopyrite free gold interpreted as the last mineralizing event occurs as late fracture filling in the pervasive silicification zone

reservoir characterization using surface microseismic monitoring microseismic monitoring of reservoir processes can be performed using surface or near surface arrays we review the published technical basis for the use of the arrays and the historical development of the method beginning with locating earthquakes through geothermal exploration to the growing field of hydraulic fracture monitoring practical considerations for the array deployment and data processing are presented the road ahead for the technology includes a move toward life of field buried arrays as well as opportunities for extended interpretation of the data particularly inversion for source mechanism estimation and measurement of anisotropy in the monitored subsurface

gold and trace element zonation in pyrite using a laser imaging technique implications for the timing of gold in orogenic and carlin style sediment hosted deposits laser ablation icp ms imaging of gold and other trace elements in pyrite from four different sedimenthosted gold arsenic deposits has revealed two distinct episodes of gold enrichment in each deposit an early synsedimentary stage where invisible gold is concentrated in arsenian diagenetic pyrite along with other trace elements in particular as ni pb zn ag mo te v and se and a later hydrothermal stage where gold forms as either free gold grains in cracks in overgrowth metamorphic and or hydrothermal pyrite or as narrow goldarsenic rims on the outermost parts of the overgrowth hydrothermal pyrite compared to the diagenetic pyrites the hydrothermal pyrites are commonly depleted in ni v zn pb and ag with cyclic zones of co ni and as concentration the outermost hydrothermal pyrite rims are either as au rich as in moderate to highgrade deposits such as carlin and bendigo or co ni rich and as au poor as in moderate to low grade deposits such as sukhoi log and spanish mountain the early enrichment of gold in arsenic bearing syngenetic to diagenetic pyrite within black shale facies of sedimentary basins is proposed as a critical requirement for the later development of carlin style and orogenic gold deposits in sedimentary environments the best grade sediment hosted deposits appear to have the gold climax event toward the final stages of deformation related hydrothermal pyrite growth and fluid flow

velocity anisotropy in shales a petrophysical study using ultrasonic velocity and anisotropy measurements on a variety of shales with different clay and kerogen content clay mineralogy and porosity at a wide range of effective pressure we find that elastic anisotropy of shales increases substantially with compaction the effect is attributed to both porosity reduction and smectite to illite transformation with diagenesis a means of kerogen content mapping using velocity versus porosity crossplot for shales is shown matrix anisotropy of shales dramatically increases with kerogen reaching the maximum values of about 0 4 at total organic carbon toc 15 20 a strong chemical softening effect was found in shales containing even minor amounts of swelling smectite clay when saturated with aqueous solution this effect results in a significant p wave anisotropy reduction as compared to dry and oil saturated shales since mature black shales are normally oil wet this effect can only have a local significance restricted to the wellbore wall accurate measurements of phase velocities including velocities at a 45 direction to the bedding plane allow us to immediately calculate elastic stiffnesses and anisotropic parameters intrinsic high pressure properties of shales display an e 0 relation introduction of the bedding parallel microcracks in overpressured shales results in a decrease when fully fluid saturated and a increase when partially gas saturated with a characteristic effect on the shape of the p wave velocity surface at small angles of incidence filtering the contribution of the intrinsic anisotropy of shales it is possible to estimate the pore fluid phase microcrack density and aspect ratio parameters using seismic anisotropy measurements