shell mounds as environmental proxies on the southern coast of brazil despite the multiple constraints of using shell mounds for building relative sea level rsl curves one of the premises behind this use is still valid in modern archaeological research this refers to the sites being continuously built near bodies of water rich in fish species and mollusk beds studies that combine the evolution of settlement patterns with the geological evolution of coastal areas in brazil reach analogous results the distribution of shell mounds in time and space follows the landscape transformations induced by rsl variations through the holocene although shell mounds are not precise indicators of rsl they provide evidences of the paleo geographical changes during the holocene of which rsl is one of the many control variables by collecting and transporting mollusks to the shell mounds humans inevitably carry sediments from the substrate where mollusks live for example the beaches and lagoons near the sites in this work the geoarchaeological study of three shell mounds located in the southern coast of santa catarina state combined with mollusk taxa identification show the direct association of shell mound content with the changing landscape the predominance of ostrea sp versus anomalocardia brasiliana the presence of colluvial versus lagoonal sediments and the occurrence of echinoid spines versus muddy aggregates with diatoms gastropods and glauconitic clay characterize the distinction between sites built before and after the maximum holocene transgression respectively this attests the potential of geoarchaeological analyses in shell mounds as a complementary proxy for paleo environmental reconstructions

experimental calibration of the aluminum in hornblende geobarometer with application to long valley caldera california volcanic rocks a new geobarometer based on the al content of igneous hornblendes in equilibrium with melt fluid biotite quartz sanidine plagioclase sphene and magnetite or ilmenite has been calibrated experimentally the calibration was performed by equilibrating the required phase assemblage over the pressure range 2 8 kbar at 740 780c and then analyzing euhedral hornblendes in equilibrium with glass melt experiments were performed on natural samples of both volcanic and plutonic rocks earlier empirical calibrations of this geobarometer relied on analyzing natural hornblendes from plutons with the required phase assemblage and inferring pressure from nearby metamorphic country rocks the experimental calibration differs from the empirical calibrations especially above 5 kbar and shows that the al content of hornblendes in equilibrium with the required phase assemblage is greater for a given total pressure than previously thought the geobarometers uncertainty is dramatically reduced the derived equation is p plus minus 0 5 kbar 3 minus 3 46 plus minus 0 24 4 23 plus minus 0 13 al sup t the geobarometer is applied to post bishop tuff volcanic rocks from long valley caldera california and reveals that most rhyodacites in this complex erupted from depths of about 6 km these eruptions occurred over 500 000 yr suggesting that the rhyodacitic magma reservoir beneath longmore valley had reached a steady p depth t state less

closed system burial diagenesis in reservoir sandstones examples from the garn formation at haltenbanken area offshore mid norway abstract the middle jurassic garn formation of the haltenbanken area has been studied using mineralogical and geochemical data from 21 wells ranging in burial depths from 2 0 to 4 1 km relative to seafloor rsf k feldspar and plagioclase contents show variations on a regional scale both laterally and as a function of burial depth the content of pore filling authigenic illite increases sharply and the content of k feldspar and kaolinite decreases in garn sandstones presently at depths greater than 3 6 3 7 km rsf 120 130 c the depletion in k feldspar below 3 7 km rsf is not accompanied by lower potassium values in the bulk chemical composition wt k2o this suggests that the potassium released during k feldspar dissolution is retained in the sandstones and is precipitated as illite the variations in bulk contents of potassium and sodium are therefore considered to be related principally to primary variations in sandstone mineralogy the shallower sandstones 1 3 have a k feldspar kaolinite ratio greater than one the deeply buried 3 7 km rsf sandstones with similar potassium contents contain excess k feldspar and most of the kaolinite is illitized however deeply buried sandstones containing an average of 0 38 wt k2o k al molar ratio 1 4 contain a significant amount of kaolinite but negligible k feldspar this suggests that the k feldspar kaolinite ratio before the onset of illitization was less than one and hence that the kaolinite illite reaction has been restricted by an insufficient supply of potassium absence of k feldspar this illustrates how illitization of kaolinite depends upon k feldspar as a local source of potassium prediction of illitization in sandstones therefore must be based on integration of models for provenance facies and early diagenesis in addition to burial and thermal history the formation of pore filling authigenic illite in these sandstones is an important influence on the total reservoir quality

geochronology of early to middle proterozoic fold belts in northern australia a review abstract this geochronological review integrates geologically relevant isotopic data from the several early to middle proterozoic fold belts of northern australia a number of firm chronological benchmarks largely established by means of u pb zircon studies now provide a time framework within which to better quantify the tectonostratigraphic history of many of these terranes the apparent worldwide dearth of crustal events in the earliest proterozoic between 2500 and 2000 ma was broken in northern australia with the advent of a major crust forming episode between 1880 and 1850 ma ago these rocks may have evolved from an initial mantle or lower crustal melting and fractionation process about 400 300 ma earlier that is evidenced from sm nd model ages the extent involvement and or degree of assimilation of any pre existing archaean crust is small but whether or not it is negligible or zero is not satisfactorily known the 1880 1850 ma event the barramundi orogeny is well represented in northern australia both lithologically and analytically and the rocks that pre and post date it have a similar tectonic setting over very wide areas of the continent two consistent and widespread elements of this tectonism are regional metamorphism and deformation of the first cycle of supracrustals barramundi orogeny and crystallization of i type k rich felsic magmas closely following and in some cases overlapping with deformational processes in the halls creek inlier the ages of this rapid deep crustal to supracrustal tectonic transition cannot be distinguished within the range 1860 1850 ma this major yet short lived tectonism is mirrored in other fold belts such as pine creek tennant creek and mount isa in which u pb zircon ages give slightly older constraints of 1885 1870 ma 1920 1870 ma and 1885 10 ma respectively the ensuing felsic magmatism in these latter terranes continued for a few tens of millions of years with the crystallization and emplacement of comagmatic volcanic plutonic pairs throughout in the interval 1870 1860 ma in the georgetown and arunta inliers direct evidence of this otherwise ubiquitous event if present is masked by younger high grade metamorphism in the latter however metamorphic crustal components having approximate protolith ages of this order can be inferred from their evolved isotopic signatures the geochronological and geochemical coherency of the extensive early proterozoic 1870 ma magmatism contrasts with that of post 1800 ma magmatism which is less extensive generally anorogenic commonly bimodal in character and varies in age from one terrane to another several major sedimentary basins were being filled at this time major igneous events at 1790 1740 ma 1670 ma and 1500 ma are recognized elongate sublinear volcanic and plutonic belts 1790 1740 ma old are present at mount isa in high grade granitic gneisses of the arunta inlier a few u pb zircon ages and extrapolated rb sr protolith ages are coincident at about 1760 1750 ma indicating that this event may be important in the development of the division 2 sequences of that fold belt the platformal hart dolerite and oenpelli dolerite two of the largest mafic intrusions in the world were emplaced at 1762 25 ma and 1688 13 ma younger felsic plutonism and volcanism gave rise to rapakivi type granites in the mount isa tennant creek and the granites tanami inliers at 1670 ma a time close to that of the aileron deformational metamorphic event in central australia further at 1650 ma there is growing evidence of an unexpectedly coherent hydrothermal episode that reset or disturbed many rb sr ages gave rise to pegmatites and was possibly associated with mineralization in the davenport and eastern arunta inliers discrete middle proterozoic deformational events between 1610 and 1470 ma punctuate the tectonostratigraphic history in the arunta mount isa and georgetown fold belts where they are best documented

tectonic evolution of the pine creek inlier northern territory the pine creek inlier c 66 000 km2 contains early proterozoic sediments and volcanics deposited 1900 ma ago in a basin formed by crustal extension of c 2500 ma granitic basement about 10 km of supracrustals accumulated in 20 ma in shallow marine to continental environments during sagging related to post extensional subsidence deposition in this pine creek geosyncline was succeeded by an orogenic period lasting for 180 ma 1870 1690 ma the top end orogeny felsic and mafic intrusives were emplaced before and after the main deformation which ranged in style from open to tight upright folds in low grade areas in the centre of the region to reclined multiple isoclinal folds in areas of medium to high grade metamorphism in the northeast and west during late orogenesis rift related felsic volcanics and continental sediments were deposited on the metamorphosed sequence to form the katherine volcanic sequence representing a second period of crustal extension the lower part of this sequence was itself mildly deformed by the last significant perturbation of the top end orogeny the hiatus between these early proterozoic events and middle proterozoic deposition is marked by a saprolitic weathered profile indicating a stable subaerial period perhaps as long as 150 ma the cover rocks are the basal part of the mcarthur basin sequence which extends eastward into queensland in the pine creek region they are plateau forming sandstone generally 600 m thick thickening to 2000 m in basins near katherine formed by further movement of the late early proterozoic rift systems the region has remained stable since proterozoic time with only minor reactivation of rift structures to allow accumulation of locally thicker mesozoic and eocene sequences and intrusion of minor mafic to intermediate dykes in the late proterozoic and palaeozoic later eustatic movement led to incursion of shallow palaeozoic and mesozoic seas

material flux and porosity changes during sediment diagenesis understanding the changes in porosity that occur during burial of sediments is of importance both in modelling fluid flow in sedimentary basins and for prediction of petroleum reservoir quality when deposited up to 50 of the volume of sands is intergranular pore space porosity generally decreases with depth because of compaction and precipitation of diagenetic minerals but some sandstones retain an anomalously high porosity whether this is due to dissolution and removal of material or to its local redistribution is not clear we originally intended to quantify losses of major chemical components during burial of a complete sedimentary unit we have investigated ten reservoir sandstones of permian to tertiary age from oilfields worldwide these show consistent results and here we present detailed data from four of them we found that the silica content of these sandstones actually increased by 220 to 350 kg m 3 following compaction no statistically significant changes were observed for aluminium potassium or sodium the flux of silica cannot be modelled satisfactorily using currently accepted values of permeability silica solubility and flow rates posing a challenge for existing models of fluid flow and ore emplacement

the batman and quigleys gold deposits of the mt todd yimuyn manjerr mine australia structural petrographic and mineralogical investigations of coeval quartz sulphide vein and lode stockwork systems abstract the mt todd mine renamed the yimuyn manjerr in august 2000 in the northern territory of australia is located at the southern end of the pine creek inlier pci the mine is host to several discrete ore bodies that strike nne within a broad ne trending corridor of gold mineralisation these deposits exhibit a spatial association with local granite plutons and in particular are situated within the intermediate contact metamorphic aureole of the tennysons leucogranite they exhibit a marked difference in ore style ore system and dominant sulphide mineralogy the batman and quigleys deposits of the mt todd mine are located 4 5 km apart within the ne trending corridor of gold mineralisation the batman deposit comprises a stack of discontinuous steeply west dipping sheetlike veins within an ore envelope that defines a broad zone of normal faulting it constitutes a quartz pyrrhotite pyrite dominant system of 500 m depth continuity the quigleys deposit comprises a series of discontinuous east dipping lodes that are interconnected and subtended by stockwork veins within a single continuous fault plane the deposit constitutes an arsenopyrite pyrite dominant system of limited depth continuity despite their differences detailed structural petrographic and mineragraphic studies of the vein lode systems have established that the deposits are similar in vein lode morphology principal orebody forming process tectonic history alteration assemblage and relative geological timing there is broad agreement in the type of host lithofacies and an association with a ne trending regional magnetic lineament the studies suggest that mineralogic differences between the deposits are the result of a gross metal and sulphide zonation about the cullen batholith that corresponds with decreasing temperature and increasing distance from the margin of the batholith as noted by other workers the deposits are therefore interpreted to have formed at the same time in response to similar structural and tectonic controls gold mineralisation in the mt todd mine is thereby constrained to a single mineralising event the quartz sulphide veins and lodes of the batman and quigleys deposits are typified by hydrothermal fracturing and or normal faulting of the upper crust during sinistral strike slip displacement on a ne trending basement strike slip fault the deposits are similar to other orogenic gold deposits within the pci but with affinity to the thermal aureole gold style however in the batman deposit the association of gold with bismuth and reduced ore mineralogies makes this deposit unique in the pci

coastal shell middens in florida a view from the archaic period current models generally place the appearance of shell middens along florida s coasts after 5000 b p this paper argues that substantial shellfishing began at least two millennia earlier it reviews information on the earliest shell middens known in coastal florida and traces their evolution through the archaic period 10 000 3000 b p in three areas 1 the panhandle 2 the northeast and 3 southwestern florida in the panhandle estuarine exploitation was well established by 7200 b p the subsistence base included minor but consistent amounts of freshwater and terrestrial resources throughout the archaic on the northeast florida coast midden contents demonstrate that a range of terrestrial estuarine and littoral resources were being exploited by 6000 b p by 4500 b p however this diverse subsistence base was abandoned and a more targeted estuarine focus was adopted in southwest florida the earliest ca 7000 b p coastal populations gathered shellfish but the total subsistence regime is not clearly understood until 5000 4000 b p when intensive exploitation of marine shellfish and fish is recognized along the shore by 4500 b p in all three regions of florida estuarine subsistence bases supported population nucleation and the creation of monumental architecture by the end of the archaic period ca 3500 b p however the brief venture into large scale social works was abandoned in some but not all of florida as climate and or sea level regression brought significant environmental changes

amino acid racemization dating of marine shells a mound of possibilities shell middens are one of the most important and widespread indicators for human exploitation of marine resources and occupation of coastal environments establishing an accurate and reliable chronology for these deposits has fundamental implications for understanding the patterns of human evolution and dispersal this paper explores the potential application of a new methodology of amino acid racemization aar dating of shell middens and describes a simple protocol to test the suitability of different molluscan species this protocol provides a preliminary test for the presence of an intracrystalline fraction of proteins by bleaching experiments and subsequent heating at high temperature checking the closed system behaviour of this fraction during diagenesis only species which pass both tests can be considered suitable for further studies to obtain reliable age information this amino acid geochronological technique is also applied to midden deposits at two latitudinal extremes northern scotland and the southern red sea results obtained in this study indicate that the application of this new method of aar dating of shells has the potential to aid the geochronological investigation of shell mounds in different areas of the world

numerical modeling of folding in rotational strain histories strain regimes expected in thrust belts and shear zones numerical modeling of fold development in a layered anisotropic medium under various geometries of rotational strain shows that the only necessary requirement for fold growth from an initial perturbation fold instability is a component of shortening in the plane of the layering three strain regimes end member forms expected in thrust belts or shear zones where strain departs from ideal progressive simple shear were studied wrench shear gives rise to symmetrical folds with axes subparallel to the maximum extension direction combined wrench shear and thrust shear produces asymmetric folds with axes close to the extension direction strongly asymmetric folds may result from thrust shear together with a small component of shortening in the shear direction in wrench shear the folds develop without a component of extension in the profile plane

cleavage duplexes in the marcellus shale of the appalachian foreland abstract cleavage duplexes are zones of platy spaced cleavage that either parallel bedding or ramp through shale sections examples are 2 60 m thick the cleavage within the zones is generally subperpendicular to the zone boundaries but sigmoidally dragged against floor roof and internal thrusts between the well developed floor thrust and the more obscure roof thrusts of the duplexes the shale has been shortened 30 perpendicular to cleavage the thrusts are sharp strain discontinuities because both overlying and underlying shale is uncleaved and less deformed

thrust controlled gold mineralisation at the elandshoogte mine sabie pilgrim s rest goldfield south africa stratiform quartz sulphide gold veins locally termed reefs are hosted within the proterozoic transvaal sequence sedimentary succession in the sabie pilgrim s rest goldfield eastern transvaal these deposits have produced about 180 tonnes of gold and share many characteristics with those of telfer western australia detailed examination of the elandshoogte mine shows that gold deposition occurred in two stages both linked to bedding parallel thrust faulting within the sedimentary pile deformation being concentrated within incompetent shale beds interlayered within more competent units the majority of gold was introduced in the second stage of mineralisation and occurs within fractures in early formed sulphide minerals deposition of competent quartz veins accompanying early sulphide and gold mineralisation resulted in a change in deformation style within the reef zone from early shearing in shales to later duplex faulting of the quartz reef fluids accompanying faulting are implied to have transported gold and a magmatic source of mineralisation is suggested

thrust controlled gold quartz vein mineralisation at the tom s gully mine northern territory australia metasedimentary and minor metavolcanic rocks of the early proterozoic pine creek inlier rest unconformably on late archaean granitic basement three basin wide regional deformation events at ca 1885 1870 ma are recognised i w to nw verging thrusts and recumbent folds d2 ii upright open to tight doubly plunging nne to nnw trending folds d3 and iii open upright e trending folds d4 in the centre of the pine creek inlier post tectonic granites 1835 1820 ma are spatially temporally and probably genetically associated with mesothermal gold quartz vein deposits the tom s gully deposit consists of a shallowly s dipping quartz reef in graphitic shale and siltstone within the thermal aureole of the post tectonic 1831 6 ma mt bundey pluton gold mineralisation comprises two ssw plunging sulphidic ore shoots which are intimately associated with brecciation and recrystallisation of early barren quartz where early quartz is absent from the thrust gold mineralisation is not developed indicating that this secondary brittle fracturing was essential to sulphide and gold deposition the ore shoots plunge parallel to the trend of d3 fold axes the reef is hosted by a d2 thrust fault with transport to the nw d3 folds in the hangingwall and footwall decrease in amplitude toward the reef indicating that during continued e w compression the thrust acted as a decollement zone field relationships and microstructural studies suggest that quartz and sulphide were deposited in a reactivated thrust during wrench shear along several nne trending faults associated with emplacement of the mt bundey pluton

phosphate location and reaction in an archaeoanthrosol on shell mound in the lakes region rio de janeiro state brazil prehistoric shell middens called sambaquis occur along the brazilian coast but their geoarchaeological and pedological contexts remain little explored we characterized micromorphological attributes and forms of phosphate of key horizons of a soil at sambaqui we identified how pedogenesis may affect archaeological materials helping interpretations relating to the occurrence of elevated concentrations of phosphate associated with habitation micromorphology and microchemical analysis using sem eds investigated well studied horizons of these shell midden soils phosphate mobility is demonstrated by the occurrence of secondary ca phosphates in deeper strata free from artifacts below the midden ca apatite forms well defined microaggregates of illuvial chemical origin the primary sources of the ca and p have disappeared and we suggest they were organic materials and ash rather than the existing fragments of bone apatite or shells present in the overlying archaeoanthrosol the in situ preservation of denser and larger bone fragments may be attributed to the apatite rich micromass which retards ca apatite dissolution from bone fragments the presence of phosphate rich lower strata without direct anthropic inputs indicates that p leaching and precipitation as secondary forms has occurred during wet climate episodes

high resolution geochemical investigation of the bivalve shells glycymeris sp from shell mounds in jeju island korea late holocene paleoclimatic implications related to east asian monsoon climate abstract recent and shell mound bivalves glycymeris sp were collected from two sites sangmori and udo jeju island to investigate paleoceanographic conditions using high resolution stable isotope and trace element data the radiocarbon ages are about 3210 50 and 4210 60 bp for the sangmori and udo shell mounds respectively both oxygen and carbon isotopic compositions of the shell mound bivalve shells show clear seasonal cycles with depleted values during summer and the coeval trend which indicates that they were controlled by freshwater input similar ranges of both isotopes indicate that shallow seawater conditions near the sangmori and udo shell mounds are more or less similar however more negative oxygen and carbon isotope values of the shell mound bivalves than the recent counterpart suggest that surface seawater salinity near jeju island was lower due to the increase in changjiang river discharge mg contents of the recent bivalve reflect surface seawater temperature changes whereas sr and ba contents were controlled by nutrient concentrations directly influenced by changjiang river discharge geochemical data of the recent and shell mound bivalves may imply higher precipitation more intense east asian summer monsoon activity at 3 2 and 4 2 ka under the influence of the terminal stage of holocene climatic optimum in south china or may reflect smaller fluctuating peaks during its decline

shape as an outcome of formation history terrestrial laser scanning of shell mounds from far north queensland australia terrestrial laser scanning tls is a laser based surveying system that enables rapid measurement of x y z coordinate points creating an accurate representation of objects in three dimensional space we apply this technique to the survey and analysis of mounded shell matrix deposits smds near weipa in far north queensland australia eleven parameters were used to characterise the size and shape of 51 shell mounds located in one geographical area the results demonstrate substantial variation in mound size and shape and suggest patterning in mound form related to age as well as position on the landscape radiocarbon chronologies developed for a sample of the 51 mounds demonstrate that the mounds do not conform to a model of linear formation of a shell deposit suggesting mound histories are variable in both the nature of shell deposition as well as post depositional processes these results have important implications for interpreting the processes responsible for shell mound formation

testing ore deposit models using in situ u pb geochronology of hydrothermal monazite paleoproterozoic gold mineralization in northern australia the inability to establish absolute ages for gold deposition in the pine creek orogen of northern australia has led to conflicting ore deposit models ranging from intrusion related which predict that gold mineralization was synchronous with granite magmatism ca 1835 1820 ma to orogenic which place ore deposition nearly 100 m y later here we present ion microprobe u pb geochronology for a mineralized quartz reef from tom s gully mine mount bundey northern territory australia and nearby granitic rocks and associated contact aureoles isotopic dating of zircon and monazite indicates that intrusion and contact metamorphism occurred ca 1825 ma whereas hydrothermal monazite from the auriferous quartz reef gives a mean 207pb 206pb age of 1780 10 ma interpreted as the time of gold mineralization mineralization therefore postdated intrusion by 45 m y and preceded a postulated ca 1740 1730 ma cratonwide orogenic gold event by 50 m y hence neither the intrusion related model nor the recently proposed orogenic model is applicable combined with a reevaluation of age data from the nearby goodall gold deposit our data suggest that mineralization coincides with and may be related to an episode of regional low grade metamorphism deformation and fluid circulation shoobridge event our results demonstrate the importance of high precision in situ geochronology and detailed petrography for deciphering age relationships in ore deposits and of testing the veracity of models for ore formation

geoarchaeology in action a sedimentological analysis of anthropogenic shell mounds from the cape york region of australia abstract large mounded deposits of shell are prominent archaeological features across much of the north australian tropical coast many of the shell mounds are composed almost entirely of the bivalve anadara granosa linnaeus 1758 a food source for aboriginal people in the past a relatively long history of inquiry into the nature and significance of the shell mounds has focussed primarily on analysing the shell component as clues to australian aboriginal coastal economies in the past this paper presents results of new analyses on the non shell sediments examining the physical and chemical signatures of depositional and post depositional processes within shell mounds near weipa in far north queensland australia with a view to obtaining insights into how they formed and for what purposes and how their morphology structure and content may have changed since they ceased accumulating we also consider how such changes might relate to past and present environmental conditions physical and chemical analyses indicate that the primary purpose of mound building was most likely to discard the large volumes of shell resulting from a granosa harvesting and consumption post depositional diagenetic alteration has strongly influenced the present day composition and form of the shell mounds in particular the accession of carbon and silica to the mounds by environmental burning aided by strong leaching under the seasonal high rainfall conditions as such the mound chemistry is more likely to reflect modern environmental conditions rather than provide an archive of or an opening to the past

structural controls on gold bearing quartz mineralization in a duplex thrust system hyde macraes shear zone otago schist new zealand the hyde macraes shear zone in east otago new zealand is a low angle north to northeast dipping thrust system in which gold bearing quartz veins have been deposited mineralization accompanied deformation in the shear zone which is preferentially developed in graphitic pelitic schist the shear zone is a duplex system dominated by steep hinterland dipping thrust faults between well defined shallow dipping upper and lower bounding thrusts imbrication and stacking have occurred in the shear zone especially where intrashear schist is psammitic and relatively brittle this stacking contributes to lateral thickness changes from 2 up to 125 m mineralized veins formed mainly in dilational jogs or localized extensional zones on the relatively shallow dipping parts of the intrashear thrust faults late stage shallow south dipping extensional veins crosscut the duplex structures but are related to the same overall deformation from analysis of the shear zone structure it is possible to make predictions about the geometry of mineralized schist within unexposed parts of the shear zone this is a potentially useful tool for further prospecting and mining in hydrothermally mineralized duplex systems

turbidite hosted gold mineralization at the dolaucothi gold mines dyfed wales united kingdom the dolaucothi gold deposit occurs in thin bedded turbidites of upper ordovician to basal silurian age deposited near the southern margin of the lower paleozoic welsh basin the host rocks were deformed during the caledonian orogeny 390 410 ma into a series of inclined asymmetrical commonly overturned tight southeast facing folds with associated cleavage reverse dip slip faults accompanied the folding and the whole area is cut by late tensional faults the mineralization is controlled by structures produced during the caledonian orogeny in particular a thrust fault which formed the host to the roman lode a flat lying auriferous quartz reef up to 6 m thick gold occurs in a variety of hosts including pyritic shales containing both euhedral and framboidal pyrite quartz carbonate stringer veins in steeply or gently inclined veins associated with shear zones and in planar quartz veins associated with the roman lode the mineralogy is simple with pyrite and arsenopyrite being the dominant sulfides ankeritic carbonates hydromuscovite and the lithium silicate cookeite are also present it is proposed that during prograde metamorphism associated with early stages of the caledonide orogeny fluids circulated through the basement below the southeast margin of the welsh basin and leached gold and associated metals from rocks of igneous or volcanic origin these overpressured fluids were released to high crustal levels during later orogenic movements and uplifts perhaps related to reactivation of such basement faults as the infra tywi fault geothermometric studies indicate that the host rocks experienced upper anchizone facies metamorphism whereas the temperatures of the mineralizing fluids were in the range of 345 degrees to 450 degrees c isotopic studies point to a common origin for the sulfides in both the shales and the veins and also indicate that the host rocks provided the source of the carbon now incorporated in the carbonates