pb isotope fingerprinting of mesothermal gold deposits from central victoria australia implications for ore genesis new pb isotope data from three major mesothermal lode gold deposits ballarat west tarnagulla maldon in central victoria support a model whereby the metals derived from a large reservoir with a long residence time in the crust below the palaeozoic lachlan fold belt the pb isotopic ratios of least radiogenic samples from these deposits are in close agreement with published pb signatures for turbidite hosted gold deposits and for devonian granites elsewhere in the lachlan fold belt despite their spatial distribution and variations in the geological setting the pb signatures point to the extraction and transport of metals from a crustal source area by long lasting large scale hydrothermal systems resulting in the prominent homogenisation of pb isotopic ratios the enduring interaction between large hydrothermal systems and an extensive crustal source reservoir were a vital pre requisite in the formation of the victorian gold province in this regard the prospectivity of victoria is analogous to world class ore provinces elsewhere such as the archaean yilgarn block in western australia

regional structural controls of gold mineralisation bendigo and castlemaine goldfields central victoria australia the bendigo and castlemaine goldfields are classic examples of structurally controlled orogenic gold deposits in the bendigo zone of central victoria se australia detailed mapping and biostratigraphic interpretation has led to a better understanding of the regional structural controls of this type of gold quartz mineralisation mineralised quartz veins are hosted by the castlemaine group an early to middle ordovician turbidite succession at least 3 000 m thick gold deposits are controlled by low displacement faults that are clustered into several belts the goldfields indicating a regional structural control the timing of mineralisation overlapped with that of the major period of deformation including folding cleavage development and regional faulting the bendigo and castlemaine goldfields are located in an area termed the whitelaw thrust sheet bounded by two unmineralised high displacement regional scale faults mapping has revealed an interrelationship between the regional scale faults regional structural style and goldfield location the goldfields lie immediately west of the boundary between the upper and lower portions of the thrust sheet and are characterised by symmetric folds with sub horizontal to synclinal enveloping surfaces relatively low co axial strains and moderate cleavage development the non gold bearing areas immediately east of each goldfield correspond with the lower part of the whitelaw thrust sheet and are characterised by higher non coaxial strains stronger cleavage and folds with wide west dipping limbs giving rise to easterly vergent sections and steeply west dipping enveloping surfaces that mineralisation was an integral part of the thin skinned style of deformation in the central bendigo zone is indicated by timing relationships and the interrelationship between local scale mineralised structures and regional scale features such as large displacement unmineralised faults regional variations in fold style and overall thrust sheet geometry the work supports previous models that suggest mineralised fluids were focussed along a linked system of deep seated faults the primary conduits may have been major regional scale intrazone faults which are inferred to sole into detachments near the base of the castlemaine group it is proposed that these structures linked with minor intrazone faults and then with networks of low displacement mineralised faults that were strongly controlled by folds the location of minor intrazone faults was probably controlled by internal thrust sheet geometry the distribution of gold deposits and of gold production suggests that maximum fluid flow was concentrated along the eastern margins of networks of low displacement faults

chronology of deformation within the turbidite dominated lachlan orogen implications for the tectonic evolution of eastern australia and gondwana ar ar data from fabric forming white mica in slates syntectonic quartz veins and granitic mylonites constrain the timing of metamorphism deformation and exhumation in the lachlan orogen australia these data also help define the tectonic evolution of the tasmanides during paleozoic time the lachlan orogen formed by the progressive accretion of a thick turbidite fan sequence and volcanic terrains to gondwana during the closing of a small marginal ocean or back arc basin this tectonic setting was similar to the present western and southwestern pacific region accretion of the lachlan orogen to gondwana occurred by closing of the basin system by subduction accretion processes and some translation the process is typified in the western lachlan orogen by a major eastward migrating deformation involving chevron folding and faulting over an eastward propagating decollement melange zone and is recorded by ar ar mica ages ranging from 455 ma in the western part to 390 ma in the eastern part in the central lachlan orogen deformation migrated southwestward from 440 430 to 405 ma away from the high temperature wagga omeo metamorphic complex where deformation metamorphism occurred between 440 and 400 ma in the north 400 ma mica ages record deformation and inversion of structures in the cobar basin in the eastern lachlan orogen ar ar mica dates range from 450 to 340 ma ages of 455 445 ma are yielded by the narooma accretionary complex 405 390 ma ages are found along the major thrust faults bounding high grade metamorphic complexes and 360 340 ma cooling ages are found in the inverted extensional basins e g hill end and related structural zones the ar ar results also document periods of reactivation on early formed structures during later deformation elsewhere in the orogen

source requirements for the golden mile kalgoorlie significance to the metamorphic replacement model for archean gold deposits the golden mile at kalgoorlie represents a giant archean hydrothermal gold system localized by ductile shear zones and hosted mainly by a differentiated tholeiitic sill chlorite carbonate and pyrite alteration zones cover the whole mineralized area 1 km 3 km and calculations suggest that for the golden mile production around 1200 t au the amounts of components added to these alteration zones are 340 mt co2 20 mt k and 5 mt s if one adopts a metamorphic replacement model for gold mineralization in which all ore components derive from devolatilization of greenstones at amphibolite facies or above these data suggest that a source area involving a 5 km thick greenstone slab of area 8 km 8 km could produce the necessary co2 k s h2o and au this is considered a reasonable volume of greenstone belt and under such a model the minimum spacing of large gold deposits would be approximately 20 km along strike neither special au enriched source rocks nor unreasonably large volumes of greenstone b

fluid substitution for thinly interbedded sand shale sequences using the mesh method abstractgassmann s fluid substitution model is intended for a monomineralic homogeneous porous rock in which pore pressures induced by applied loads can equilibrate throughout the pore space these assumptions are violated when gassmann s equations are applied to measurements that represent effective medium averages over subresolution layers of alternating sand and shale the conventional procedure for treating this problem has been to first downscale i e estimate the properties of the fine scale sand and shale endmembers from the coarse scale measurements apply gassmann s fluid substitution to the sand only and then backus average back to the original scale this procedure however is very sensitive to errors in estimated sand fraction and shale properties and becomes particularly unstable at small sand fractions a new method for fluid substitution combines rock physics models for dispersed and interbedded sand shale systems which are often approximated with reuss or lower hashin shtrikman inte

tectonothermal history of the western lachlan fold belt australia insights from white mica studies detailed b lattice parameter and illite crystallinity ic studies of k white micas in slates from the stawell and ballarat bendigo zones sz bbz in the western lachlan fold belt of victoria australia reveal a metamorphic pattern characterized by regional metamorphism associated with crustal thickening and younger contact metamorphism accompanied by deformation the ic data indicate that rocks regionally metamorphosed prior to the intrusion of the early and late devonian granitoids vary in grade from epizonal greenschist facies to diagenetic zeolite facies and that most are of epizonal to anchizonal prehnite pumpellyite facies grade in the bbz a decrease in grade from west to east occurs across fault zones ic values show little change indicating that limited vertical displacement has occurred this is in accord with the thin skinned deformation model proposed for the western lachlan fold belt the b lattice parameters x 9 022 a n 137 s n 0 009 indicate baric conditions intermediate between those of new hampshire p al 2 sio 5 triple point and otago intermediate p thus a moderately low geother mal gradient existed 450 430 ma ago when these rocks were deformed k d fe mg actinolite fe mg chlorite values 0 52 0 70 obtained from coexisting actinolite and chlorite in metabasites from fault zones support the moderately high p c 4 kbar metamorphism suggested by the b cell parameter values the metamorphic conditions indicated by these data are contrary to the low p high t conditions pro posed by previous authors who inferred an intimate association between deformation granitoid intrusion and gold mineralization the b lattice parameter of white micas in slates adjacent to early devonian c 400 ma granitoids with schist bearing aureoles in the north eastern part of the bbz x 9 002 a n 27 s n 0 007 indicate pressures in the order of c 2 5 kbar which are in accord with those obtained from andalusite cordierite and zoisite garnet bearing assemblages observed in the higher grade metapelitic and calcareous rocks this contrasts with the higher pressure c 4 kbar existing during regional metamor phism and implies that c 6 5 8 km of metasedimentary rocks in the bbz were removed before the emplacement of the early devonian granitoids metamorphic assemblages in hornfelses associated with late devonian granitoids indicate a further 5 6 km of metasediment were removed in the next 40 ma prior to their emplacement this study shows the value of white mica studies in elucidating the tectono thermal history of a low grade metamorphic terrane dominated by metapelitic rocks

supergene ore and hypogene nonore mineralization at the nagambie sediment hosted gold deposit victoria australia the nagambie gold deposit central victoria australia consists of approximately 7 million metric tons of ore averaging 1 2 g t gold mineralization is confined largely to east west and n 50 degrees e oriented shears and faults contained in a doubly plunging anticlinal dome of undifferentiated silurian and early devonian siltstones and shales ore is associated with an east west trending anticlinal axis and is particularly concentrated in two east northeast trending structural zones the central and 303 shear zones five stages of protore vein genesis have been identified the first two a b are barren crenulated massive quartz primary gold mineralization occurs in stibnite bearing quartz stockwork stringers which belong to the third c and fourth d quartz veining stages whereas the fifth consists of unmineralized small veins e fluid inclusion studies on the two gold mineralization stages c and d yield trapping temperatures and pressures of 280 degrees or 25 degrees c and 1 000 to 1 200 bars and 200 degrees or 30 degrees c and 700 to 1 000 bars respectively the mineralization fluids contain h 2 o co 2 0 69 mole ch 4 0 21 mole and trace n 2 with wt percent nacl equiv values in the range of 0 to 10 2 wt percent calculated delta 18 o values 15 0 6 8 and measured delta d data 88 to 99 of the hypogene fluids indicate a meteoric origin these fluids underwent extreme 18 o enrichment by reacting with country rocks metamorphic or igneous genesis of the ore as opposed to the protore is as secondary supergene enrichment accompanied by varying degrees of surficial limonite alteration ore mineralization occurs almost exclusively in limonitized fractures up to 60 m below the surface in and adjacent to major shears based on features such as the spatial distribution high purity 999 26 fine and the form of the gold and its close association with limonite it is proposed that the gold is mobilized by surficial leaching and concentrated near the water table vertical movement of the water table perhaps due to seasonal changes as well as erosion produces rapid dissolution of hypogene gold and or aurostibite from above or at the water table

syn metamorphic gold mineralisation invincible vein nw otago schist new zealand the invincible vein fills a fault zone which strikes northeast and dips steeply southeast in the lower rees valley nw otago the vein cuts north striking foliation in lower greenschist facies otago schist structures associated with the fault zone are both brittle and ductile and the fault zone has had a complex history of post mineralisation reactivation mineralised vein material filling parts of the fault zone consist of quartz albite muscovite chlorite calcite pyrite arsenopyrite and minor gold these minerals have been strained and locally recrystallised during ductile deformation fluid inclusion homogenisation temperatures 140 175 c and ice melting temperatures 0 to 1 c indicate that the mineralising fluid was low salinity low co2 water with a density between 0 88 and 0 93 g cm3 arsenopyrite geothermometry implies a temperature of mineralisation of 370 70 c mineralisation pressure lay between 2 and 5 kbar mineralisation pressure temperature conditions and mineralogy are essentially the same as for metamorphism of the host schist vein calcite oxygen isotope ratios 12 to 15 per mil are similar to host schist values carbon isotope ratios of vein calcite 3 to 5 per mil are distinctly different from ratios in host schist 7 to 10 per mil elevated vein cr contents and isotopically depleted carbon data are consistent with some degree of equilibration with metavolcanic rocks it is inferred that metavolcanic rocks of the underlying aspiring terrane were a significant source for mineralising fluid and metals invincible mineralisation occurred in the latter stages of metamorphism and is the earliest recognised gold bearing vein system in the otago schist

upper eocene palynoflora from łukowa se poland and its palaeoenvironmental context abstract this paper presents the results of a palynological investigation of the sands from upper eocene priabonian epicontinental marine strata at ukowa se poland this locality represents an isolated spot of upper eocene strata in the southern part of epicontinental poland due to later uplift and erosion of this area the sands studied yielded a well preserved palynoflora providing information about palaeovegetation and palaeoclimate after the early eocene climate optimum during the study a total of 94 fossil species of palynomorphs were identified the results indicate that the vicinity of the sedimentary basin was covered by vegetation with a significant portion of thermophilous taxa and containing many elements with east asian affinities the plant communities were composed of platanus platycarya engelhardioideae members of the hamamelidaceae sapotaceae fabaceae oleaceae fagaceae probably evergreen quercus and castanoideae and betulaceae families as well as salix carya and others members of the pinaceae family and sciadopitys were components of coniferous or mixed forests taxodium and presumably glyptostrobus together with nyssa might have covered areas with a higher groundwater level the pollen of milfordia and aglaoreidia cyclops can probably be considered as representing marsh freshwater vegetation cryptogams are represented mainly by ferns including members of the lygodiaceae and schizaeaceae probably as well as gleicheniaceae and cyatheaceae families and lycopodiaceae including lycopodiella the presence of frequent pollen and spores of the genera presently growing under tropical and subtropical climatic conditions and the presence of several taxa characteristic for swamps indicate that the climate during deposition of the sediments studied was warm and humid the mean annual temperature of 17 2 23 1 c was estimated on the basis of coexistence approach method

divergent double subduction tectonic and petrologic consequences divergent double subduction involving removal of an oceanic basin from both sides and collision has distinct fingerprints of magmatism and significant implications for the tectono magmatic evolution of orogenic belts the complete evolution of a divergent double subduction system involves four stages 1 initial interaction between the two divergent subduction zones on both sides of a single oceanic plate 2 closure of the oceanic basin when the two overriding plates meet followed by 3 detachment of the oceanic lithosphere from the overlying crust and sedimentary sections 4 sinking and disappearance of the oceanic slab into the mantle detachment of the oceanic slab leads to intense decompressional melting of mantle and triggers melting of accretionary wedge strata and lower crust resulting in large scale magmatic and volcanic activity the main consequences of a divergent double subduction system are that it produces opposed thrust systems extensive long lived granitoid magmatism with mantle isotopic signature and volcanism that evolves toward bimodalism this model can be applied to the western half of the paleozoic lachlan fold belt southeastern australia to explain the wide scale silurian to early carboniferous granitoid magmatism its spatial and temporal relationships and late bimodal magmatism closure of the oceanic basin is thought to have occurred during the early to middle devonian detachment of the oceanic slab led to felsic to intermediate composition magmatism bimodal volcanism involving local basaltic flows is a reflection of subsequent sinking of the slab

the coexistence approach a method for quantitative reconstructions of tertiary terrestrial palaeoclimate data using plant fossils abstract the coexistence approach is introduced as a method for quantitative terrestrial palaeoclimate reconstructions in the tertiary it is based on the assumption that tertiary plant taxa have similar climatic requirements to their nearest living relatives the aim of the coexistence approach is to find for a given fossil flora and a given climate parameter the climatic interval in which all nearest living relatives of the fossil flora can coexist for this purpose we have developed a data base climbot containing for over 800 tertiary plant taxa the nearest living relatives and their climatic requirements and an algorithm for analysis climst for all types of fossil floras the coexistence approach thus allows the rapid quantitative reconstruction of 10 different climate parameters including the mean annual temperature temperature of the warmest month temperature of the coldest month mean annual precipitation maximum monthly precipitation minimum monthly precipitation precipitation of the warmest month relative humidity potential evaporation as well as the ratio of mean annual precipitation over potential evaporation the reliability and resolution of the coexistence approach are tested with various techniques and proved to be reasonably good for instance the resolution with respect to the mean annual temperature can be up to 1 c applications to various modern and fossil floras are illustrated and the advantages and disadvantages of the coexistence approach are discussed

sediment hosted gold deposits in guizhou china products of wall rock sulfidation by deep crustal fluids sediment hosted gold deposits in guizhou china are hosted in late paleozoic and early mesozoic sedimentary rocks along the southwest margin of the precambrian yangtze craton they have characteristics similar to carlin type gold deposits in nevada and are notably enriched in as sb hg and tl the shuiyindong and yata deposits consist of disseminated strata bound sulfides in permian bioclastic limestone and fault controlled mineralization in middle triassic calcareous clastic rocks respectively mineralization in both deposits consists of barren milky quartz veins disseminated gold bearing arsenian pyrite and arsenopyrite stibnite realgar and orpiment the barren milky quartz veins occur in the ore controlling structures with an envelope of gold mineralization in the host rock consisting of disseminated gold bearing arsenian pyrite and arsenopyrite and replacement style quartz veinlets later drusy quartz stibnite realgar and orpiment fill fractures and vugs on the periphery of gold mineralization petrography microthermometry laser raman spectroscopy and laser ablation inductively coupled plasma mass spectrometric la icp ms analyses of fluid inclusions are used to characterize the chemical evolution of ore fluids at shuiyindong and yata early barren milky quartz veins trapped aqueous fluid with moderate salinity 6 0 wt nacl equiv and minor co2 2 4 mol at a temperature of 230 30 c this fluid contains measurable b na k cs sr as sb and au 3 8 0 5 5 7 2 3 g g determined by la icp ms and is interpreted to approximate the mineralizing fluid responsible for precipitation of early barren quartz veins low salinity 0 9 2 3 wt nacl equiv co2 bearing 6 3 8 4 mol aqueous fluids are recorded in replacement style quartz veinlets they formed gold bearing arsenian pyrite and arsenopyrite and quartz veinlets at a temperature of 210 20 c and pressures of 450 to 1 150 bars corresponding to depths between 1 7 and 4 3 km under lithostatic conditions fluid inclusions in late stibnite orpiment realgar quartz veins contain high co2 58 64 mol and n2 19 2 23 7 mol with trace ch4 up to 1 6 mol the increasing content of co2 and decrease in the concentrations of au and as in aqueous carbonic inclusions are interpreted to result from carbonate dissolution at the level of the deposits during gold mineralization covariance of au as sb and sr concentrations in the fluids is interpreted to reflect deposition of as and sb sulfides and gold concurrent with carbonate crystallization iron is below detection limit 400 g g in all fluid inclusion types suggesting that the ore fluids were fe poor but possibly sulfur rich possibly explaining their exceptionally high gold contents iron in sulfide minerals was probably derived from dissolution of ferroan minerals in the host rocks sulfidized by h2s rich fluids to precipitate arsenian pyrite arsenopyrite and gold pressure fluctuation induced by faulting resulted in local fluid immiscibility and led to late deposition of realgar orpiment stibnite and calcite hydrogen and oxygen isotope compositions of ore fluids d h2o 35 to 68 18o h2o 4 16 5 indicate a metamorphic origin possibly related to crustal thickening and prograde metamorphism during the late yanshanian orogeny

timing of gold mineralisation in western and central victoria australia new constraints from shrimp ii analysis of zircon grains from felsic intrusive rocks abstract age constraints provided by felsic intrusive rocks indicate that gold mineralisation in western and central victoria australia occurred over a prolonged period of time ranging from prior to the late silurian to the late devonian an early phase of gold mineralisation associated with regional deformation pre dated the emplacement of late silurian felsic porphyry dykes at 413 3 ma in the central lode system of the magdala deposit stawell gold mineralisation associated with the final stages of the main regional deformation also pre dated the intrusion of early ca 400 ma to late devonian ca 370 ma plutons at stawell wonga deposit mt bute tarnagulla tallangalook maldon and heathcote in both the stawell pyrenees and ballarat metallogenic provinces consistent with preliminary dating studies of hydrothermal micas from major gold deposits later phases of gold mineralisation throughout western and central victoria were either temporally associated with or post dated the intrusion of late silurian to late devonian felsic dykes examples of this style of mineralisation include the wonga deposit at stawell mafeking fosterville maryborough minor occurrences near linton and the woods point region preliminary constraints from ballarat west indicate that late devonian dykes intruded at ca 386 ma were pervasively altered by interaction with an auriferous fluid similar to that responsible for gold deposition within the guiding star lode but that this was probably related to remobilisation during emplacement of the dykes into a pre existing mineralised structure with the exception of the woods point region and ballarat west these later phases often have a magmatic affiliation indicated by an association with cu mo bi sb and w these complex timing relationships reflect the diachronous nature of deformation metamorphism and magmatism in the western lachlan fold belt of southeast australia and suggest at least two discrete periods of gold mineralisation in the region

formation of gold deposits review and evaluation of the continuum model abstract the continuum model has been one of the more widely advocated genetic models for gold only deposits such as those found in archaean greenstone belts it postulates that hydrothermal gold deposits were formed throughout a 20 25 km vertical crustal profile from temperatures above 700 c to below 180 c and that the deposition occurred synchronous with the peak of metamorphism the continuum model is reviewed at this stage because we believe that it does not successfully account for many aspects of gold deposit formation the most obvious shortcoming is in considering ore deposits found in rocks of uppermost amphibolite and granulite facies domains where temperatures were appropriate for partial melting the main chemical condition that favours melting is access to h2o from either aqueous fluid or the breakdown of hydrous minerals a major gold forming hydrothermal event at the peak of high grade metamorphism as implied by the continuum model is incompatible with partial melting of wallrocks instead of forming a hydrothermal gold deposit an aqueous fluid introduced during partial melting would be consumed to produce further melt five gold deposits are documented from high metamorphic grade domains within four separate archaean cratons one is the type example used in the continuum model the other four have been significant producers partial melting has been recorded in the wallrocks adjacent to gold mineralisation at big bell hemlo challenger and renco gold deposits in the sulphide rich ore itself at challenger and hemlo deposits and as cross cutting dykes and migmatites at griffins find for these five deposits and indeed in general the continuum model does not easily account for aspects of the fluid source fluid composition gold transport and metal deposition the evidence that has been used to support deposit formation at the peak of high grade metamorphism as required by the continuum model is generally compatible with one or more alternative genetic models textural and structural siting of the gold high variance mineral assemblages proportion of various gold host rocks and relative element enrichments at high metamorphic grade can be accounted for by gold formation at greenschist facies conditions followed by progress of the deposit to high metamorphic grade metamorphic model moreover the type examples in the continuum model of deposits in sub greenschist facies domains appear to be incorrectly ascribed and are likely to be in greenschist facies domains the continuum model does not adequately explain archaean gold deposits

reconstruction of vegetation transects for the messinian piacenzian of italy by means of comparative analysis of pollen leaf and carpological records abstract the first comprehensive and comparative analysis of the main micro pollen and macro leaves fruits and seeds palaeobotanical data from northern and central italian sites allows four transects of ancient vegetation for the messinian to piacenzian interval to be constructed standard criteria for the reconstruction of vegetation transects are established so that our approach could be extended to other basins or regions bearing neogene palaeofloras and would permit readily comparable reconstructions of past vegetation to be obtained messinian to piacenzian lowland plant communities as reconstructed by means of this integrated and standardized approach show the dominance of warm temperate forest taxa in northern and central italy with the highest floristic affinity to present day forests of the eastern part of central china some panholartic conifers usually interpreted as cool temperate taxa in neogene assemblages are assigned to the upland vegetation they are scarcely represented in messinian and zanclean pollen records with the exception of some intervals characterized by increases in picea and cedrus and almost completely lacking in leaf and carpological ones during the piacenzian notably from 2 8 ma the pollen percentage of such taxa in particular picea progressively increased the overall scantiness of non aquatic herbs not only in the macrofossil record but also in the pollen one indicates the absence of dry conditions and excludes long lasting expansion of open vegetation the type of vegetation subtropical humid forest reconstructed for the evaporitic messinian ca 5 9 to 5 6 ma suggests that the adriatic padane basin would have been under predominant moist conditions even during the deposition of evaporites slightly drier phases in the post evaporitic messinian are suggested at first by the short period of increase of lygeum a steppe plant close to 5 5 ma then by the ecological preferences of some unusual macrofossil taxa cupressus medicago vitex these are however still associated with arboreal plants which require humid conditions definitely indicating that forested environments persisted subtropical sub humid forest the zanclean and piacenzian transects are extremely similar to the evaporitic messinian one and the mesic lowland zonal vegetation can still be defined as subtropical humid forest

possible intrusion related gold systems in the western lachlan orogen southeast australia several gold deposits occurring in the western lachlan orogen have geological geochemical and geochronological characteristics that distinguish them from typical vein hosted orogenic gold deposits of the central victorian gold province the latter are responsible for more than 90 percent of primary hard rock gold production from this region and are generally considered to represent the only economically significant type of gold deposit in the western lachlan orogen atypical gold occurrences at malmsbury myrtle creek mount piper and the wonga deposit in the stawell goldfield are characterized by a close spatial and temporal association with posttectonic felsic intrusions disseminated to stockwork style mineralization alteration dominated by sericitization sulfidation silicification carbonatization and tourmalinization and associated complex au mo w bi te cu the deposits have a number of features in common with intrusion related gold deposits elsewhere in phanerozoic orogenic belts although production from this type of gold mineralization in the western lachlan orogen has been small compared to orogenic gold deposits the possible existence of intrusion related gold deposits has potentially important implications for exploration in this region and also provides significant clues to the tectonic framework and paleozoic metallogeny of eastern australia

geologic framework and tectonic evolution in western victoria australia abstract the stawell zone is interpreted to be part of the eastern extension of the adelaide fold belt into victoria the cambro ordovician turbidite sequence of the stawell and glenelg zones rests on a pile of late proterozoic metavolcanic rocks rather than cambrian metavolcanic units that are characteristic of the lachlan fold belt early deformation events d 1 d 3 in the stawell zone pre date granite emplacement and were synchronous with regional fold forming events that accompany thrust movements along discrete detachment surfaces the thrust system follows a ne se trending strike with an e directed translation of the tectonic units the steep 60 predominantly w dipping thrusts represent high strain zones localised in relatively weak cambro ordovician quartz rich turbidites that are sandwiched along the boundaries of the late proterozoic metavolcanics overprinting the early thrust system are d 4 d 6 deformation events that include reverse strike slip and normal faults the grampians extensional basin overlying the late proterozoic to ordovician sequence records a significant change in the tectonic regime operating during the late silurian early devonian it has been subjected to a middle devonian compressional deformation event d 4 with the development of thrust and fold structures this deformation is also superimposed on the thrusted and folded d 1 to d 3 sequence to the east of the grampians half graben producing further thrusts a gradual change from a ne sw to a n s stress field produces oblique strike slip faults normal faults of probably early cretaceous age transect the entire sequence the proterozoic cambrian sequence has been affected by a low p high t mid greenschist facies regional metamorphic event peak metamorphic conditions have been inferred from metavolcanic rocks and mafic units derived from a strongly differentiated tholeiitic suite at stawell these have been calculated to be 1 7 0 7 2 kbar and 450 20 2 c the advective heat input necessary to create this low p high t metamorphic event is attributed to penetrative deformation and strain partitioning between the crust and the mantle lithosphere which in turn causes crustal thickening associated compression and the observed d 1 to d 3 structures on the surface

do extant nearest relatives of thermophile european cenozoic plant elements reliably reflect climatic signal abstract climatic characteristics of selected extant relatives and analogues for palaeotropical and neotropical european cenozoic plant elements are compared with the proxies derived from comparisons of complete plant assemblages containing the respective elements with analogous extant vegetation the discrepancies obtained may warn us not to lay too much stress on such actualistic data methodologies relying on autecology of the nearest living relatives may thus produce biased and possibly unrealistic proxies the differences in climatic estimates derived from physiognomical methodologies e g leaf margin analysis and clamp may be explained in this way but more studies in approximations between the neogene and extant analogous vegetation and climate are needed to provide more objective data

wall rock petrology and geochemistry in alteration halos associated with mesothermal gold mineralization central victoria australia integrated petrological and geochemical examination of metasedimentary assemblages associated with mesothermal lode gold mineralization in five major centers of past and present production ballarat percydale tarnagulla maldon fosterville in central victoria australia reveal that hydrothermal alteration in the hosting cambro ordovician turbidites is much more pronounced and extensive than has previously been recognized characteristically the auriferous reef structures are surrounded by bleached zones up to several tens of meters wide sericitization carbonatization and carbonate spotting and pyrite and arsenopyrite porphyroblasts within and beyond zones of visible bleaching are the most obvious features of alteration quantitative xrd analysis illustrates that these marked bleached halos are due to the replacement of albitized plagioclase clasts by white mica and the breakdown of metamorphic chlorite to form secondary carbonates and to a lesser extent kaolin the negative correlation between metamorphic chlorite and hydrothermal carbonate phases provides a reliable mineralogical alteration index useful to exploration geochemical reconnaissance profiles also indicate the development of systematic trends in response to hydrothermal alteration involving mainly sio2 k2o na2o co2 as au and s at constant bulk rock volume calculation of a geochemical alteration index given by the ratio k2o co2 k2o co2 na2o al2o3 suggests that this can be a reliable indicator of alteration in particular where concentrations of individual invariable oxides such as al2o3 vary too much in response to lithological variations saturation indices that are based on ratios of 3k al and co2 mg fe ca are less reliable because muscovite and carbonate are not always the dominant alteration mineral species of relevance the alteration assemblages as well as mineralogical and geochemical trends at the five ore systems investigated herein are common to many slate belt hosted gold deposits the results of this investigation show that although the detection of such systematic spatial variations relative to mineralization can be complicated for example by postore modification of the wall rocks due to contact metamorphism e g at maldon or where mineralization is not associated with massive to laminated quartz veins e g at fosterville recognition of extensive though not always conspicuous alteration halos around mesothermal lode gold mineralization represents a potentially powerful tool for exploration in slate belts

tectonic constraints on the timing relationships of metamorphism fluid production and gold bearing quartz vein emplacement abstract there is an ongoing discussion about the genetic significance of the postmetamorphic emplacement of many gold mineralizations as a contribution to this discussion this paper reviews the timing relationships between metamorphic devolatilization and metamorphism at different crustal levels for different tectonic processes for example denudation accompanying or following thickening causes metamorphism to occur later at depth than at shallow levels thus many internally heated terrains e g barrovian terrains are of deep later type that is peak metamorphism and devolatilization at deeper levels occurs at later times metamorphic processes of the deep later type may produce and release metamorphic fluids during prograde metamorphism at depth and precipitate them in the form of postmetamorphic quartz veins at shallow levels magmatic heating from below on the other hand is a deep earlier process causing inverse timing relationships in many metamorphic terrains deep later and deep earlier processes may compete for example if denudation at the surface accompanies heating from below if denudation and heating from below are of similar duration deep later characteristics prevail and a strongly bi modal age distribution of peak metamorphism in different crustal levels may arise the upper crust will experience metamorphism early but largely contemporaneously and the lower crust will experience metamorphism much later this process is particularly favourable for substantial simultaneous devolatilization of large sections of the lower crust to postdate metamorphism at shallow levels thus such processes may result in late infiltration events in cooling rocks of low metamorphic grade the common observation of postmetamorphic fluid infiltration and mineralization may therefore indicate but does not require that the mineralising fluids are related to the same metamorphic event

metallogenic relationships to tectonic evolution the lachlan orogen australia abstract placing ore formation within the overall tectonic framework of an evolving orogenic system provides important constraints for the development of plate tectonic models distinct metallogenic associations across the palaeozoic lachlan orogen in se australia are interpreted to be the manifestation of interactions between several microplates and three accretionary complexes in an oceanic back arc setting in the ordovician significant orogenic gold deposits formed within a developing accretionary wedge along the pacific margin of gondwana at the same time major porphyry cu au systems formed in an oceanic island arc outboard of an evolved magmatic arc that in turn gave rise to granite related sn w deposits in the early silurian during the ongoing evolution of the orogen in the late silurian to early devonian sediment hosted cu au and pb zn deposits formed in short lived intra arc basins whereas a developing fore arc system provided the conditions for the formation of several volcanogenic massive sulphide deposits inversion of these basins and accretion to the australian continental margin triggered another pulse of orogenic gold mineralisation during the final consolidation of the orogenic belt in the middle to late devonian

deposit density of tungsten polymetallic deposits in the eastern nanling metallogenic belt china abstract estimation of the number of undiscovered mineral deposits is critical for quantitatively assessing mineral resources traditional statistic methods are limited to analyzing the spatial distribution of mineral deposits which can be considered spatial point processes because of complexity self organized criticality and singularity properties in this study spatial statistic methods including average nearest neighbor distance fry analysis k function and fractal analysis are used to quantify the agglomeration and fractal characteristics of tungsten polymetallic deposits in the eastern nanling metallogenic belt enmb local singularity analysis for w sn mo bi be association is used to delineate the permissive areas for tungsten deposits the results show that tungsten polymetallic deposits are distributed with fractal clustering in region while at random in permissive areas the summary function comparison shows that the k function analysis based on a heterogeneous process may be more robust than on a homogeneous k function when quantifying the distribution of mineral deposits especially for endogenic deposits furthermore the concept of mineral equivalent is introduced in this study and the combination of mineral equivalent and radial density model for mineral deposits mitigates the problem of ignoring the proportion of large medium and small sized deposits in the uniform deposit density model the estimation results indicate that there are still good future prospects in this region this research not only extends the application of spatial statistics in quantifying the spatial distribution of mineral deposits but also provides a new approach to estimate the number of undiscovered mineral deposits

vegetation and climate development of the new jersey hinterland during the late middle miocene iodp expedition 313 site m0027 abstract we investigated the palynology of sediment cores from site m0027 iodp exp 313 45 km off the present day coast of new jersey to infer palaeoenvironmental conditions during the second half of the mid miocene climatic optimum and the transition to global cooler conditions in sum 79 taxa were identified via light microscopy 13 gymnosperms 63 angiosperms 3 pteridophytes among them diospyros and reevesia which until now have not been identified from the eastern coast of north america most of the identified taxa belong to the extended multi layered broadleaved mesophytic forest that occupied the lowlands of the new jersey hinterland and reflects the zonal vegetation during time of deposition in higher altitudes or on edaphically drier slopes the mesophytic forest was replaced by conifer forest landscape changes probably induced the spread and diminution of several vegetation units during the late middle miocene an expansion of a conifer forest from 15 8 to 15 6 ma is probably connected to the appalachian uplift and a subsequent spreading of cupressaceae between 15 0 and 14 8 ma probably reflects a period of enhanced inundation of coastal lowlands the modern representatives of the main climatic elements among the encountered taxa are characterized by a typical temperate distribution climatic parameters mat cmmt wmmt map were calculated using bioclimatic analysis in light of the ongoing discussion concerning identifications of cupressaceae pollen grains two different variations of the bioclimatic analysis were performed both variations indicate humid warm temperate climatic conditions with mean annual temperatures of 13 c 5 c coldest month temperatures of 4 3 c 5 3 c and warmest month temperatures of 21 9 c 4 5 c annual precipitation values exceed 1000 mm for all samples both zonal vegetation and the calculated regional lowland palaeoclimate show no significant changes one factor creating generally climatically stable conditions between 15 8 and 12 7 ma was likely the buffering effect of the gulf current loop

what is shale to a petrophysicist what is a shale in a recent presentation to the geophysical society of houston rune holt attempted to answer the question by listing three attributes of a shale 1 clay minerals should constitute the load bearing framework 2 shales have nanometer pore sizes and nanodarcy permeability 3 surface area is large and water is adsorbed on surfaces or bound inside clay platelets this is a good definition of shales but perhaps a typical geophysicist may not know how to apply it in practice with typical data sets in particular a geophysicist often has no core data and is limited to well logs this article describes how petrophysicists traditionally distinguish sands from shales using typical well logs in clastic sections only lean shales with minimal organic content are considered here

evidence for externally derived vein forming and mineralising fluids an example from the magdala gold mine stawell victoria australia abstract mineralogical and microfabric studies of the magdala gold deposit together with isotopic and fluid inclusion studies have shown that the mineralising fluid is externally derived the host rocks to the quartz veins do not possess any significant amounts of gold whereas the quartz veins can contain 7 g t gold the walls to the quartz veins possess alteration haloes in the form of stilpnomelane porphyroblasts attesting to the fact that the fluid in the veins was out of equilibrium with the host rocks the distribution of alteration haloes that occur parallel to the quartz vein margins necessitates that a subvertical fluid gradient be more or less constant during the deposition process in order to produce the observed architecture of the alteration haloes quartz lodes possess 18 o values that range from 15 8 to 17 3 per mil while associated host rocks range between 9 7 to 12 per mil in the metabasalts and 10 2 to 14 1 per mil in the volcanogenic and metasedimentary rocks the dissimilarity of 18 o values between host rocks and quartz veins suggests that there has been a high fluid influx in the veins implying external buffering four types of fluid inclusions were distinguished on the basis of spatial arrangement and composition using the laser raman spectroscopy method the salinity of the fluid inclusions range from 0 7 to 8 4 wt nacl equivalent suggesting that gold was deposited due to the influx of different external fluids the association of pyrite arsenopyrite pyrrhotite with gold and with pges suggests that these fluids have a lower crustal origin and may have originated from the upper mantle and mixed with fluids derived from deep seated metasediments

a compositional classification for grain assemblages in fine grained sediments and sedimentary rocks reply abstract a tripartite compositional classification is proposed for sediments and sedimentary rocks that have grain assemblages with greater than 50 percent of a weight or volume of particles smaller than 62 5 m 4 phi tarl terrigenous argillaceous contains a grain assemblage dominated by more than 75 percent of particles of extrabasinal derivation including grains derived from continental weathering and also volcanogenic debris carl calcareous argillaceous contains less than 75 percent of particles of extrabasinal derivation debris and among its intrabasinal grains contains a preponderance of biogenic carbonate particles including carbonate aggregates sarl siliceous argillaceous contains less than 75 percent of particles of extrabasinal derivation and contains a preponderance of biogenic siliceous particles over carbonate grains these three classes of fine grained particulate sediments and rocks effectively separate materials that have distinct depositional settings and systematic contrasts in organic matter content and minor grain types in the subsurface the grain assemblages that define these classes follow contrasting and predictable diagenetic pathways that have significant implications for the evolution of bulk rock properties and thus assigning a fine grained rock to one of these classes is an important first step for predicting its economic and engineering qualities for purposes of description these three class names can be joined to modifier terms denoting rock texture more precise compositional divisions specific grain types of notable importance and diagenetic features

distribution of orogenic gold deposits in relation to fault zones and gravity gradients targeting tools applied to the eastern goldfields yilgarn craton western australia a quantitative spatial analysis of mineral deposit distributions in relation to their proximity to a variety of structural elements is used to define parameters that can influence metal endowment deposit location and the resource potential of a region using orogenic gold deposits as an example geostatistical techniques are applied in a geographic information systems based regional scale analysis in the high data density yilgarn craton of western australia metal endowment gold production and gold rank per square kilometer is measured in incremental buffer regions created in relation to vector lines such as faults the greatest metal tonnages are related to intersections of major faults with regional anticlines and to fault jogs particularly those of dilatant geometry using fault length in parameter search there is a strong association between crustal scale shear zones faults and deposits nonetheless it is the small scale faults that are marginal or peripheral to the larger scale features that are more prospective gravity gradients depicted as multiscale edges or gravity worms show a clear association to faults that host gold deposits long wavelength long strikelength edges interpreted as dominantly fault related have greater metal endowment and provide a first order area selection filter for exploration particularly in areas of poor exposure statistical analysis of fault fold and gravity gradient patterns mainly affirms empirical exploration criteria for orogenic gold deposits such as associations with crustal scale faults anticlinal hinge zones dilational jogs elevated fault roughness strong rheological contrasts and medium metamorphic grade rocks the presence and concurrence of these parameters determine the metallogenic endowment of a given fault system and segments within the system by quantifying such parameters the search area for exploration can be significantly reduced by an order of magnitude while increasing the chance of discovery

link between gold provinces low salinity high temperature 200 degrees c reducing fluids are poorly represented in ore forming processes yet appear to account for 90 percent of the primary gold mined to date such fluids have been implicated in the formation of many archcan greenstone witwatersrand slate belt and epithermal gold deposits these low salinity auriferous fluids occur in variable time space lithological sequence and tectonic settings and are most easily explained by metamorphic devolatilization of mafic and or graywacke successions metamorphism of chlorite calcite albite quartz assemblages e g mafic or graywacke at the greenschist amphibolite facies boundary occurs around 480 degrees or 20 degrees c for 3 5 kbars and produces large volumes of low salinity h 2 o co 2 fluid similar in composition to those recorded in many gold deposits widespread pyrite in the above assemblage typically leads to elevated levels of dissolved sulfur such conditions are ideal for gold transport as a molecular au s complex and can lead to deposits rich in gold relative to silver and base metals deposition of gold occurs in the temperature range of 250 degrees to 400 degrees c and can be facilitated by lower temperature lower sulfur activity and changes in oxygen activity lower sulfur activity is most readily achieved by fluid interaction with fe rich host rocks with the formation of pyrite or pyrrhotite whereas lower oxygen activity is readily achieved by interaction with carbonaceous metasediments low salinity fluids produced by metamorphic devolatilization provide a common theme embracing the formation of many archcan greenstone slate belt witwatersrand and potentially epithermal gold deposits it involves the common features of high geothermal gradient low salinity fluid high au ag high au base metals and broad synchroneity with metamorphism it also accounts for the considerable variability in hosting structures detailed timing relations host rocks alteration assemblages and geologic age of different deposits interestingly the similarities are explained by deeper processes the differences by processes at or near the depositional sites

the geology and gold deposits of the victorian gold province abstract the palaeozoic succession of victoria represents a major world gold province with a total production of 2500 t of gold i e 78 million oz on a global scale central victoria represents one of the most gold mineralized areas outside the witwatersrand of south africa and remains the prime example of a slate belt gold province also known as turbidite hosted or shale greywacke gold province production came from quartz veins 1000 t modern placers 1200 t and palaeoplacers 300 t up to 7000 mines produced gold from quartz veins however the 168 mines of this type which produced over 1 t au contributed 68 of the primary gold production twelve goldfields have each produced 30 t au approximately one million ounces from all sources with bendigo 697 t ballarat 408 t and castlemaine 173 t being the largest these twelve goldfields have contributed 71 of the combined primary and secondary production gold mining commenced in 1851 declined dramatically around 1914 and has not increased significantly since the palaeozoic succession of victoria is part of an extensive fold belt along much of eastern australia i e the tasman orogenic belt in victoria the succession is dominated by cambrian to early devonian clastic metasedimentary rocks that have undergone major upright deformation and low grade metamorphism culminating in the middle devonian tabberabberan orogeny north south inliers of cambrian metavolcanic and metasedimentary rocks associated with regional fault zones divide the province into several geologically distinct zones in central victoria there are particularly well developed acid volcanic complexes of late devonian age and synchronous peraluminous granites which represent high temperature crustal melting tertiary to quaternary basalts have covered some of the palaeozoic gold deposits and have also covered several rich gold placer deposits of cainozoic age larger goldfields including bendigo and ballarat occur in ordovician slate and greywacke sequences but a wide range of metamorphosed sedimentary and igneous rock types are host to goldfields most if not all primary deposits demonstrate structural control although the controlling structural features differ between deposits wallrock alteration is strongly influenced by host rock in metasedimentary rocks it is limited and subtle but it is more pervasive in mafic and felsic igneous rocks carbonates muscovite and pyrite are the most widespread alteration minerals in these rocks representing co 2 k and s addition enrichment of as within gold deposits is common with sb important in some small deposits whereas base metals are only abundant locally and bi w mo and te show strong spatial association with granites and are rarely associated with economic gold deposits granites are an important component of the palaeozoic succession in victoria no large deposits are within granites but a few goldfields including maldon 65 t au are within contact aureoles of either s or i type granites of differing degrees of fractionation and silica content a single stage but protracted and possibly diachronous period of gold introduction near the time of the middle devonian tabberabberan deformation can explain geological relationships at many gold deposits the possibility that this event was slightly older i e silurian or early devonian in the west of the state cannot be precluded from the available evidence the mineralizing event appears linked to the same thermal event as diorite lamprophyre dykes and graite intrusions acidic and basaltic volcanism deformation and regional metamorphism the limited amount of fluid chemistry data from victorian gold deposits suggests low salinity fluids which contained co 2 and variable methane with homogenization temperatures from 150 to 300 c the sulphur isotopic compositions of pyrite are mostly 1 to 5 with some values slightly above 10 mineralizing temperatures are inferred to be near 300 c and pressure around 1 2 kbar sulphide rich gold deposits in the east of victoria many of which contain significant base metals contrast with the rest of the province which contains mostly gold deposits with lower sulphide content and this eastern area should possibly be viewed as separate from the victorian gold province per se the benefits to victorian gold mining coming from the 1980 s global gold boom have been insignificant compared to the historical importance of the victorian gold province there seems little justification for assuming that all the large deposits have been discovered and there is reason to believe new deposit styles may emerge to complement the limited current exploration activity which is focussed on the search for extensions and repeats of known deposit types a major advance in scientific understanding of these oft neglected deposits could kindle a major exploration and production revival

metatholeiites and interflow sediments from the cambrian heathcote greenstone belt australia sources for gold mineralization in victoria metatholeiites and interflow sediments of cambrian age are exposed in the lake cooper quarry located in the northern segment of the heathcote greenstone belt central victoria australia the exposed sequence is 281 m thick and comprises nine massive to pillowed lava flows and seven interflow sequences the metabasalts from the lake cooper quarry have strong petrological and geochemical similarities to normal midocean ridge basalts n morb and to metabasalts from greenstone suites elsewhere in victoria suggesting that they have not been exposed to extensive hydrothermal alteration the interflow sediments in the quarry are subdivided into units comprising finely bedded sulfides layers of sulfidic carbonaceous argillites chert and sedimentary carbonate rocks unusual mineral assemblages in these sediments as well as their trace element concentrations and rare earth element signatures suggest an exhalative volcanogenic origin whereas gold values in the tholeiites from the lake cooper quarry generally remain below 2 to 5 ppb gold contents in the interflow sediments which are also characterized by elevated as cu and zn values range from 5 to 243 ppb and average 67 ppb on the basis of sedimentological features and sulfide petrology accumulation of the ore metals in these sediments is inferred to have occurred during deposition of the exhalative precipitates possibly as a result of extraction and transfer of ore metals from the thick boninite sequence known to occur below the tholeiites in victoria mass balance calculations show that remobilization of gold from the interflow sediments by metamorphic fluids and subsequent redeposition within dilatation zones and structural traps at higher crustal levels during the early to middle paleozoic could account for a significant component of the central victorian gold province thus these exhalative metasediments might have played a vital role in accumulating preconcentrating and providing the gold required to form the world class turbidite hosted lode deposits in the lachlan fold belt of victoria

metamorphism in archaean greenstone belts calculated fluid compositions and implications for gold mineralization an inescapable consequence of the metamorphism of greenstone belt sequences is the release of a large volume of metamorphic fluid of low salinity with chemical characteristics controlled by the mineral assemblages involved in the devolatilization reactions for mafic and ultramafic sequences the composition of fluids released at upper greenschist to lower amphibolite facies conditions for the necessary relatively hot geotherm corresponds to those inferred for greenstone gold deposits xco2 0 2 0 3 this result follows from the calculation of mineral equilibria in the model system cao mgo feo al2o3 sio2 h2o co2 using a new expanded internally consistent dataset greenstone metamorphism cannot have involved much crustal over thickening because very shallow levels of greenstone belts are preserved such orogeny can be accounted for if compressive deformation of the crust is accompanied by thinning of the mantle lithosphere in this case the observed metamorphism which was contemporaneous with deformation is of the low p high t type for this type of metamorphism the metamorphic peak should have occurred earlier at deeper levels in the crust i e the piezothermal array should be of the deeper earlier type however at shallow crustal levels the piezothermal array is likely to have been of deeper later type as a consequence of erosion thus while the lower crust reached maximum temperatures and partially melted to produce the observed granites mid crustal levels were releasing fluids prograde into shallow crustal levels that were already retrograde we propose that these fluids are responsible for the gold mineralization thus the contemporaneity of igneous activity and gold mineralization is a natural consequence of the thermal evolution and does not mean that the mineralization has to be a consequence of igneous processes upward migration of metamorphic fluid via appropriate structurally controlled pathways will bring the fluid into contact with mineral assemblages that have equilibrated with a fluid with significantly lower xco2 these assemblages are therefore grossly out of equilibrium with the fluid in the case of infiltrated metabasic rocks intense carbonation and sulphidation is predicted if as seems reasonable gold is mobilized by the fluid generated by devolatilization then the combination of processes proposed most of which are an inevitable consequence of the metamorphism leads to the formation of greenstone gold deposits predominantly from metamorphic fluids

the relative roles of folding and faulting in controlling gold mineralization along the deborah anticline bendigo victoria australia gold mineralization along the deborah anticline bendigo australia occurs in quartz veins that are categorized into two main groups those associated with folds and those associated with faults the relative chronology of the structural development and quartz vein emplacement is characterized by the initial development of the fold and the subsequent formation of bedding and cleavage parallel veins saddle reefs may have developed at this stage reverse faults and their associated veins formed after folds had locked up major gold hosting structures include saddle reefs reverse faults and composite fold fault structures where reverse faults have disrupted saddle reefs some reverse faults are interpreted to have propagated along preexisting structures such as bedding parallel veins although gold is hosted in fold related structures the majority is found in veins associated with later faults folds and fold related veins strongly controlled the location of these later formed reverse faults and their associated veins a fault based fracture system was superimposed on preexisting dilational sites such as bedding parallel veins and saddle reefs and it is possible that this allowed for the introduction of a larger volume of fluids during faulting than was possible during folding

genetic implications of stable isotope characteristics of mesothermal au deposits and related sb and hg deposits in the canadian cordillera the canadian cordillera hosts a large number of mesothermal au or ag vein deposits the deposits are scattered throughout accreted and suspect terranes of the cordillera and often have a distinct spatial association with strike slip faults these vein deposits possess a striking degree of homogeneity in delta 18 o values on vein district and regional scales in most districts delta 18 o values for mineralized quartz veins vary only by 2 to 3 per mil across the entire district over the canadian cordillera as a whole delta 18 o values for such veins range from 13 to 18 per mil smow in contrast to the high degree of homogeneity evident in the delta 18 o values of the veins alteration zones in adjoining wall rocks possess distinctive zoning patterns indicating isotopic exchange between ore fluids and host units deposits of hg and sb are also closely associated with strike slip faults in the canadian cordillera area the delta 18 o studies of quartz from these deposits indicate average values of 29 or 2 0 per mil smow for quartz from the hg deposits and 21 0 or 1 5 per mil for quartz from the sb deposits when corrected for isotopic fractionation assuming equilibrium conditions average delta 18 o values for ore forming fluids of the various deposit types all fall within a 5 per mil range indicating a probable common fluid source for the three deposit types all three deposit types have delta 13 c values for carbonates in the range of 10 to 2 per mil pdb which are believed to reflect a heterogeneous source for the carbon the delta d values from serpentinites associated with au deposits and inclusion fluids from all three deposit types are lighter than 100 per mil and latitudinally dependent indicating the involvement of chemically evolved meteoric water in the ore forming process a model for formation of these deposits is presented involving the convection of meteoric water in the brittle crust to depths of 12 to 15 km and temperatures of 300 degrees to 400 degrees c during descent the fluid evolves in delta 18 o and acquires constituents involved in the later ore forming process fluids ascend in highly permeable zones associated with strike slip faults depositing quartz sulfides and au at a depth of approximately 10 km and a temperature of 300 degrees or 50 degrees c at shallower levels and cooler temperatures sb quartz or au veins are formed and near the surface cinnabar and carbonate are deposited at temperatures near 150 degrees c similarities in geology and geochemistry of mesothermal au deposits of the canadian cordillera and deposits of the mother lode california and the archecan cratons suggest that the model proposed herein may also be applicable to those deposits

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

spatial data analysis of mineral deposit point patterns applications to exploration targeting abstract systematic spatial analysis of mineral deposit point patterns can reveal significant spatial properties of mineral systems with major implications for regional mineral prospectivity modelling for valid results a study area needs to be clearly defined taking into account permissiveness of the geological units for a particular mineral system and effects of cover standard statistical tests assuming an isometric contiguous study area with regionally homogeneous distribution of deposits are likely to produce invalid results analysis of regional uniformity of spatial deposit density is required for adequate design and interpretation of tests for clustering spatial distribution of orogenic gold deposits in the hodgkinson province in queensland and the western lachlan orogen in victoria australia indicates the presence of significant regional linear metallogenic zones probably controlled by deep crustal domain boundaries oblique and not related to any recognised major faults within the metallogenic zones in both regions individual gold occurrences are strongly clustered into ore fields but the distribution of ore fields is random

character and kinematics of faults within the turbidite dominated lachlan orogen implications for tectonic evolution of eastern australia reply fault zones within turbidite dominated orogenic systems typified by the lachlan orogen of eastern australia are characterised by higher than average strain and intense mica fabrics transposition foliation and isoclinal folds poly deformation with overprinting crenulation cleavages and steeply to moderately plunging meso and micro folds they have a different character compared to the brittle ductile fault zones of classic foreland fold and thrust belts such as the appalachians and the canadian rocky mountains multiple cleavages and transposition layering record a progressive shear related deformation history an intense mica fabric evolves initially during shortening of the overlying sedimentary wedge but is progressively modified during rotation and emplacement to higher structural levels along the steep parts of inferred listric faults the deformed wedge outside the fault zones generally undergoes one phase of deformation shown by a weak to moderately developed slaty cleavage which is parallel to the axial surface of upright subhorizontally plunging chevron folds other faults within the turbidites of the lachlan orogen include the steep zones of ductile strike slip deformation that bound a centrally located high t low p metamorphic complex characterised by s c mylonites these ductile shear zones indicate a southward passage of the metamorphic complex as a crustal wedge with emplacement to higher structural levels along a leading edge ductile thrust fault ar ar dating constrains the timing of regional deformation to be mostly late ordovician through silurian across the lachlan orogen faults in the low grade turbidite sequences record the kinematic evolution of the developing lachlan orogen and indicate progressive deformation associated with simultaneous eastward propagating and migrating deformation fronts in both the western and eastern parts of the fold belt these deformation fronts are related to accretionary style deformation at the leading edges of overriding plates in an inferred southwest pacific type subduction setting from the late ordovician to the mid devonian along the former gondwana margin the fault zones effectively accommodate and preserve movements within the structurally thickening migrating and prograding accretionary wedge

mossman orogenic gold province in north queensland australia regional metallogenic controls and undiscovered gold endowment the hodgkinson and broken river provinces of the mossman orogen in north queensland host numerous orogenic gold deposits and still remain under explored this paper discusses regional metallogenic controls and results of a probabilistic quantitative assessment of undiscovered gold potential in the region significant orogenic gold deposits in the region occur only within relatively small well endowed metallogenic zones likely to be controlled by the eastern margin of the paleoproterozoic continental crust underlying the western mossman orogen three distinct styles of primary orogenic gold deposits are present in the area gold quartz veins refractory gold associated with quartz pyrite arsenopyrite veins and stockworks and stibnite quartz gold veins refractory gold deposits are estimated to have the highest potential for significant undiscovered resources in the region the hodgkinson province is estimated to host between one and ten significant undiscovered refractory gold ore fields with a 50 probability of at least 20 t of total contained gold and a 90 probability of at least 1 t the broken river province is estimated to host up to five significant undiscovered refractory gold ore fields with a 50 probability of at least 12 t of contained gold

miocene climate in europe patterns and evolution to improve our understanding of long term climate changes during the neogene in eurasia the international research network neclime neogene climate evolution in eurasia was established in the year 2000 in this first synthesis results of neclime activities focussing on the miocene of europe as one key area are combined to present a summary of the climate evolution in time and space more than 300 miocene fossil floras have been compiled and quantitatively analysed in terms of several climatic parameters during the last few years in this volume alone about 75 new data sets are available to synthesize the results of this volume quantitative climate maps for europe are generated on palaeogeographic maps for langhian and early tortonian for the first time characteristic climate patterns appear for each time interval and can be related to both global climate change and alpine tectonics generally the climate maps combine and support the individual results discussed in this volume for the individual regions

the coexistence approach theoretical background and practical considerations of using plant fossils for climate quantification the coexistence approach was established by mosbrugger and utescher 1997 as a plant based method to reconstruct palaeoclimate by considering recent climatic distribution ranges of the nearest living relatives of each fossil taxon during its existence for over more than 15 years its basics have been tested and reviewed in comparison with other terrestrial and marine climate reconstruction techniques and climate modelling data however some controversies remain about its underlying data or its applicability in general in view of these controversies this paper discusses the power and limitations of the coexistence approach by summarising past results and new developments we give insights into the details and problems of each step of the application from the assignment of the fossil plant to the most suitable nearest living relative the crucial consideration of the usefulness of specific taxa towards their climatic values and the correct interpretation of the software based suggested palaeoclimatic intervals furthermore we reflect on the fundamental data integrated in the coexistence approach by explaining different concepts and usages of plant distribution information and the advantages and disadvantages of modern climatic maps additionally we elaborate on the importance of continually updating the information incorporated in the database due to new findings in e g palaeo botany meteorology and computer technology finally for a transparent and appropriate use we give certain guidelines for future applications and emphasize to users how to carefully consider and discuss their results we show the coexistence approach to be an adaptive method capable of yielding palaeoclimatic and palaeoenvironmental information through rime and space c 2014 elsevier b v all rights reserved

estimation of late eocene bartonian priabonian terrestrial palaeoclimate contributions from megafloral assemblages from central germany abstract the eocene the world s last global greenhouse period shows distinct climatic developments through time from subtropical towards warm temperate conditions in europe the present paper investigates the response of five floras of the central german weiselster basin from different stratigraphic ages to terrestrial palaeoclimatic variations the floras were selected from the zeitz floral assemblage florenkomplex and cover a time interval of ca 3 5 myr within the late eocene which is supposed to be a period of gradual decline of global mean annual temperatures the zeitz floral assemblage was characterized by mainly evergreen notophyllous intrazonal vegetation consisting of subtropical and warm temperate elements the five floras as well as the entire zeitz floral assemblage have been analysed using the following quantitative techniques leaf margin analysis lma climate leaf analysis multivariate program clamp and coexistence approach ca furthermore the results have been compared with previously published estimates for additional localities from the same area and age the temperature estimates derived for the zeitz floral assemblage are in a good agreement with those of previous studies i e mean annual temperature mat 16 1 20 0 c warmest month mean temperature wmmt 24 9 26 4 c coldest month mean temperature cmmt 9 2 13 3 c deviations have been determined for the calculated mean annual precipitation map 1308 1335 mm compared to previously published data indicating values of about 2000 mm both clamp and ca reveal clear hints for seasonality in precipitation which is in agreement with previous phytosociological assumptions and palynological data the estimates for the individual sites differ between the different techniques as well as among the individual sites but generally indicate no temporal trends in temperature and precipitation development additionally the applicability of these techniques for fluvial estuarine plant assemblages as well as the applicability of intrazonal vegetation for reconstructing transregional climate conditions are discussed taphonomic and methodical biases are also subject of debate

chronology and tectonic framework of turbidite hosted gold deposits in the western lachlan fold belt victoria results abstract 40 ar 39 ar data constrain the history of metamorphism deformation and mineralization in the western subprovince of the lachlan fold belt rocks in the mount stavely volcanic complex and the bushy creek pluton give 40 ar 39 ar ages of about 500 ma for hornblende and biotite the dates from the mount stavely volcanic complex limit the age of mineralization in the metavolcanic rocks of the stavely belt whereas the date for the bushy creek pluton extends the area of cambrian ordovician plutons of the delamerian orogeny to east of the grampians mountains and helps define the surface expression of the western border of the paleozoic lachlan fold belt 40 ar 39 ar dating of metamorphic mica growth phengite in cleaved slates and phyllites within the landsborough fault avoca fault zone heathcote fault zone and mount wellington fault zone gives ages of 453 2 440 2 426 4 and 410 390 ma respectively these data indicate a progression of deformation from west to east starting in late ordovician early silurian time in the stawell and bendigo ballarat structural zones the major phase of deformation in the western subprovince of the lachlan fold belt is therefore silurian and not devonian sericites from major gold deposits in the stawell zone and bendigo ballarat zone give 40 ar 39 ar dates of about 440 ma that are coincident with folding and thrusting a second episode of mineralization and fault reactivation at about 420 to 410 ma is found in some deposits in these zones based on data from a previous study in the melbourne zone including the woods point dike swarm and locally in the bendigo ballarat zone some gold deposits give sericite dates of about 380 360 ma these ages are consistent with the close association of many melbourne zone gold deposits with devonian dikes and plutons the results indicate that gold mineralization in the stawell zone bendigo ballarat zone and melbourne zone was episodic and both temporally and spatially associated with crustal heating linked to regional metamorphism and plutonism initial stages of mineralization in the province comprising many of the large deposits in western and central victoria e g bendigo ballarat stawell wattle gully tarnagulla accompanied metamorphism folding and thrusting subsequent mineralization is widespread but produced mainly smaller deposits

a role for data richness mapping in exploration decision making abstract exploration programs involve long multi branched decision pathways with many potential outcomes from a single starting point critical decisions along this pathway include the choice of the area s in which to explore and the choice to acquire new data sets to assist in exploration included in this is a factoring of risks including the technical risks associated with imperfect data and the value relative to cost of collecting more data in our experience it is not common practice to explicitly assess and quantify the impact of data on exploration decisions a better understanding of the opportunity provided by data has the potential to improve the quality and or ease of decision making in this study we explore the potential role of data richness mapping as part of a decision making workflow we outline a method to quantitatively assess data richness following a four level hierarchy namely presence of data l1 quality of data l2 and attributes of data l3 measures of these are combined across several data sets to give an overall estimate of data richness l4 using this data richness map along with past exploration records and a prospectivity model we conduct an illustrative case study for gold exploration in the bryah sub basin yerrida basin region of western australia the first application is to produce a simple data based classification of regions with different technical risk characteristics the second application is to combine this with a prospectivity model to better understand exploration potential the third application uses data richness mapping to understand which data sets are most likely to have an impact on regional exploration in each case we show how an understanding of data richness can help support exploration decision making

undiscovered orogenic gold endowment in northern victoria australia abstract the northern part of the victorian gold province australia is covered by cainozoic sediments and remains poorly explored this contiguous covered area of over 44 000 km 2 is highly prospective for orogenic gold deposits this paper discusses results of probabilistic quantitative assessments of undiscovered gold potential in the northern covered parts of the western lachlan orogen the stawell bendigo and melbourne zones for the bendigo and stawell zones quantitative estimates were only made for undiscovered mesozonal orogenic gold quartz vein deposits the predominant type of gold mineralisation in that region for the northern part of the bendigo zone under cover 10 000 km 2 the mean estimate is approximately 1000 t with a 90 probability of at least 290 t of gold in undiscovered mesozonal orogenic gold deposits for the northern covered area of the stawell zone 30 000 km 2 the mean estimate is 1200 t with a 90 probability of at least 200 t of undiscovered gold the northern part of the melbourne zone 4400 km 2 is considered prospective for epizonal orogenic gold deposits associated with quartz pyrite arsenopyrite veins and stockworks or with quartz stibnite gold veins the mean estimate for that area is 90 t with a 90 probability of at least 10 t of gold in undiscovered epizonal orogenic gold deposits

gold deposits and occurrences of the greater caucasus georgia republic their genesis and prospecting criteria abstract the south central part of the greater caucasus region georgia republic represents an extremely prospective region for significant orogenic gold deposits gold bearing quartz veins are concentrated in two extensive wnw trending belts the mestia racha and svaneti districts within the northern margin of the southern slope zone of the great caucasus orogen this metalliferous region is dominated by early to middle jurassic slates which are part of a terrane that likely accreted to the continental margin from late paleozoic to jurassic the slates were subsequently intruded by both middle to late jurassic and neogene granitoids quartz veins in the more carbonaceous slate units are most consistently enriched in as au hg sb and w and show mineralization styles most consistent with typical orogenic gold deposits quartz veins in the mestia racha district were mined in soviet times for as sb and w but many of these are now being recognized as gold resource targets the veins occur in the footwall of a thrust fault between the southern slope zone and an earlier accreted terrane the main zone to the north many veins in the district continue along strike for 1 km and some cut neogene intrusions constraining ore formation to the most recent 4 to 5 million years gold deposition thus correlates with final collision of the arabian plate to the south and uplift of the ore hosting greater caucasus the zopkhito deposit previously mined for antimony contains an estimated 55 t au at a cutoff grade of 0 5 g t the veins are localized in an area where smaller order structures show a major change in strike from n s to more e w trends a pyrite arsenopyrite ore stage includes gold concentrated in both sulfide phases it is overprinted by a later stibnite dominant stage fluid inclusion studies of ore samples from the zopkhito deposit indicate minimum trapping temperatures of 300 to 350 c and 200 to 300 c for the two stages respectively and minimum trapping pressures of 0 2 to 0 5 kbar ore forming fluids with approximately 5 to 20 mol non aqueous gas evolved from n2 dominant to co2 dominant during evolution of the hydrothermal system 34s values of 1 to 4 for ore related sulfides at zopkhito are consistent with a sedimentary rock source for the sulfur and 18o quartz measurements of 16 to 21 are consistent with either a magmatic or metamorphic fluid more than 60 gold bearing lodes and placers in the svaneti district occur along the thrust between the southern slope and main zones lode gold potential was first recognized in the historic placer district in the 1980s with many auriferous quartz veins cutting middle jurassic igneous rocks brecciated veins in the 18 t au lukhra deposit cut a small granodioritic to dioritic stock the latter intrudes devonian schist immediately north of the thrust presently there are three recognized ore zones in the deposit with the most significant occurring over an area 140 m in length and 12 m wide with typical grades of 7 to 9 g t au reconnaissance fluid inclusion studies of ore samples from the lukhra deposit indicate minimum trapping temperatures of 220 c measurements of 18oquartz of about 10 suggest buffering of isotopic composition by the igneous host rocks

environmental analysis of the mid latitudinal european eocene sites of plant macrofossils and their possible analogues in east asia article i nfo previously known eocene floras of mid latitudinal europe are analysed using statistical methodologies in order to obtain more reliable palaeoclimatological signals to detect possible climatic fluctuations during this time interval only macrofossil assemblages have been taken into account and subjected to the statistical evaluation called the integrated plant record ipr vegetation analysis which is based mostly on percentages of various components additional palaeoclimatic approaches were employed namely the coexistence approach based on autecology of the nearest living relatives and the physiognomic methods of the leaf margin analysis and climate leaf analysis multivariate program clamp the same statistical approaches have been applied to analogous living vegetation of china and japan for comparative purposes additionally an update of objective statistical tools for the selection of the best suited modern vegetation clamp dataset from 144 site physg3br gridmet3br 173 physg3ar gridmet3ar and 189 physgasia1 gridmetasia1 extant biotopes is proposed including its copy paste excel application

bedding parallel veins and their relationship to folding abstract laminated bedding parallel veins hosted in turbiditic sandstone shale sequences from central victoria australia consist of stacked millimetre thick sub parallel sheets of quartz separated by micaceous layers wall rock slivers and pressure solution seams they have very high length to thickness ratios are laterally continuous over tens to hundreds of metres and have relatively uniform thickness compared to other vein types they are intimately associated with and folded by chevron folds and the quartz grain shape elongation lineation is commonly orthogonal to mesoscopic and macroscopic fold hinge lines the bedding parallel veins have two morphological forms type i are thin commonly 5 10 cm laminated veins which have complex microstructures dominated by phyllosilicate inclusion surfaces related to oblique opening along bedding with varying rates of deposition opening relative to shear displacement slip along the bedding surfaces more common are type ii thicker generally

a comparison of orogenic gold mineralisation in central victoria aus western south island nz and nova scotia can implications for variations in the endowment of palaeozoic metamorphic terrains abstract the palaeozoic western lachlan orogen in victoria se australia the buller terrane western south island new zealand and the meguma terrane nova scotia canada are remarkably similar in regard to their geological age and history structural make up and the setting and formation of orogenic lode and disseminated style gold deposits within these fold belts a comprehensive review of the principal characteristics of orogenic gold deposits in each of the three historically important gold provinces illustrates the many similarities but it also reveals several major geological structural tectonic geochemical and geochronological differences that may account for the disparity in contained gold and overall endowment between the three fold belts aspects that stand out as potentially playing a critical role in the generation of a phanerozoic world class orogenic gold province include 1 the presence of a hydrated oceanic character substrate that can provide a fertile source rock for both fluids and metals 2 asthenospheric thermal input to trigger and sustain crustal devolatilisation and melting 3 the existence of a number of near vertical deep seated faults 4 substantial transcurrent movement and 5 evolution of an accretionary subduction system that promotes development of an extensive fore arc system with prolonged fluid generation and circulation quantification of these controlling factors provide a significantly improved understanding of the processes that control the genesis of orogenic gold deposits and also have the potential to enable discrimination between more and less gold favourable orogens and parts of orogens

thrust related strain gradients and thrusting mechanisms in a chevron folded sequence southeastern australia an e directed imbricate fan thrust system within a chevron folded monotonous quartz rich turbidite succession shows marked gradients in strain from the upper to lower parts of individual thrust sheets upper parts of thrust sheets show low to moderate strains xz strains 30 1 tight inclined chevron folds ila 30 with predominantly w dipping axial surfaces intense phyllitic cleavage with a strong down dip mineral stretching lineation and long curved tapering quartz pressure shadows on pyrite such differences in fold geometry the intensity of the cleavage and the geometry of quartz fibres in pressure shadows require thrust sheet emplacement to be synchronous with the internal deformation of sheets thrust sheets show a change from an approximately constant volume plane strain coaxial deformation in their upper parts to non coaxial high strain deformation with incremental i between those expected for pure shear and simple shear i e 0 i 5 45 in their basal parts observed geometries and intensities reflect partitioning of strain and deformation mechanisms within individual thrust sheet volumes both during the initiation and propagation of subsurface detachment faults and with their emplacement to shallower crustal levels strain softening related to chevron folding and more intense cleavage development within a 500 m basal zone has controlled the emplacement of these turbidite dominated thrust sheets transport and internal deformation of the thrust sheets did not involve gravitationally induced spreading but required either a push from the rear or some form of underthrusting

a method for climatic reconstruction of the mediterranean pliocene using pollen data pollen data from numerous sites around the mediterranean sea indicate that several important vegetation and climatic changes occurred during the pliocene these data are in good agreement with pollen records from northwest europe and with 18o curves from mediterranean and atlantic deep sea cores quantitative palaeoclimatic reconstructions from pliocene pollen data of the mediterranean region cannot be based on conventional modern analogue techniques as individual pliocene pollen spectra contain taxa representing temperate warm temperate and subtropical plants that do not grow together today instead we propose a new method that uses a climatic amplitude method modified to take partially into account the relative abundances of the taxa we applied this method to the pliocene garraf 1 palynological sequence from catalonia which provides a long continuous record of climatic change from 5 3 ma to the early pleistocene we estimate that annual temperatures were 1 to 5 c higher than today and the annual precipitation 400 to 1000 mm higher than today prior to the beginning of the late cenozoic glacial interglacial cycles in contrast temperature and precipitation both fell sharply during the glacial phases of the earliest glacial interglacial cycles

a geochronological framework for orogenic gold mineralisation in central victoria australia new 40ar 39ar geochronological data support and significantly expand upon preliminary age data that were interpreted to suggest an episodic and diachronous emplacement of gold across the western lachlan fold belt australia these geochronological data indicate that mineralisation in the central victorian gold province occurred in response to episodic eastward progressing deformation metamorphism and exhumation associated with the formation of the western lachlan fold belt initial gold formation throughout the stawell and the bendigo structural zones can be constrained to a broad interval of time between 455 and 435 ma with remobilisation of metals into new structures and or new pulses of mineralisation occurring between 420 and 400 ma and again between 380 and 370 ma linked to episodic variations in the regional stress field and during intrusion of felsic dykes and plutons this separation of ages is incompatible with the view that gold emplacement in the western lachlan fold belt was the result of a single orogen wide event during the devonian a distinct phase of gold mineralisation characterised by elevated cu mo sb or w is associated with both late silurian to early devonian 420 to 400 ma and middle to late devonian 380 to 370 ma magmatism when crustal thickening and shortening during the ongoing consolidation of the western lachlan fold belt led to extensive melt development in the lower crust and resulted in widespread magmatism throughout central victoria these 420 to 400 ma and 380 to 370 ma occurrences best exemplified by the wonga deposit in the stawell structural zone and many of the woods point deposits in the melbourne structural zone but also evidenced by occurrences at fosterville and maldon in the bendigo structural zone clearly formed synchronous with or post date the emplacement of plutons and dykes and thus are spatially if not genetically related to melt generation at depth this later magmatic associated and polymetallic type of gold mineralisation is economically subordinate to the earlier metamorphic associated type of gold deposition in the stawell and bendigo structural zones but tends to be the dominant style in the melbourne zone these new geochronological constraints together with zircon u pb data from felsic intrusive rocks of known relationship to gold mineralisation demonstrate that initial hydrothermal alteration associated with gold emplacement in the western lachlan fold belt was metamorphic related predating the emplacement of granite plutons by as much as 80 million years this timing differs from other important orogenic gold districts where gold deposition is closely associated spatially with felsic magmatism the early introduction of metamorphically derived fluids well before magmatism may reflect variations in the timing of peak metamorphic conditions at different crustal levels in an accretionary prism undergoing simultaneous deformation and erosion consequently no genetic link exists between the main phase s of gold mineralisation and magmatism in the central victorian gold province with the exception of formation of a minor magmatism related and geochemically distinct mineralisation style at about 420 to 400 ma and again at about 380 to 370 ma the apparent spatial relationship between gold mineralisation and felsic intrusions is merely the result of melts and fluids being channelised along the same structures

appraisal of the usgs three part mineral resource assessment through estimation of the orogenic gold endowment of the sandstone greenstone belt yilgarn craton western australia regional scale ground selection presents a significant risk in mineral exploration targeting as any exploration search space contains a finite and fixed number of ore bodies selection of barren or depleted search spaces incurs wasted exploration expenditure by defining regions of estimated high mineral endowment via generation of quantitative information as to the value of potential discoveries mineral exploration effectiveness project acquisition and exploration portfolio management can be improved the three part mineral resource assessment developed by the united states geological survey usgs is a methodology designed to assist in this process here two separate assessments are applied to estimate the orogenic gold endowment of the sandstone greenstone belt in the yilgarn craton western australia first the results of a global regression assessment median endowment of 33 t 1 16 moz au mean of 130 t 4 59 moz au based on an available but outdated global grade tonnage model for low sulfide gold quartz vein deposits suggest that most outcropping and shallow orebodies in the sandstone greenstone belt have been discovered and fully delineated in contrast an expert assessment median endowment of 210 t 7 41 moz au mean of 220 t 7 76 moz au using expert derived grade and tonnage distributions specific to the sandstone greenstone belt predicts that significant gold mineralization remains to be discovered largely beneath cover the contrasting assessments imply a step change in exploration focus from surficial deposits at the time of the usgs global grade tonnage model to those buried under cover at the present time the expert assessment in contrast to the global regression assessment implies the potential for deeper exploration targets within the sandstone greenstone belt based on the predicted total number of deposits much of the undiscovered mineral endowment is likely to be distal to known ore bodies beneath cover and at greater depths within the belt

quantitative reconstruction of the late miocene monsoon climates of southwest china a case study of the lincang flora from yunnan province the miocene lincang leaf assemblage is used in this paper as proxy data to reconstruct the palaeoclimate of southwestern yunnan sw china and the evolution of monsoon intensity three quantitative methods were chosen for this reconstruction i e leaf margin analysis lma climate leaf analysis multivariate program clamp and the coexistence approach ca these methods however yield inconsistent results particularly for the precipitation as also shown in european and other east asian cenozoic floras the wide range of the reconstructed climatic parameters includes the mean annual temperature mat of 18 5 24 7 degrees c and the mean annual precipitation map of 1213 3711 mm compared with the modem lincang climate mat 17 3 degrees c map 1178 7 mm the miocene climate is slightly warmer wetter and has a higher temperature seasonality a detailed comparison on the palaeoclimatic variables with the coeval late miocene xiaolongtan flora from the eastern part of yunnan allows us to investigate the development and interactions of both south asian and east asian monsoons during the late miocene in southwest china now under strong influence of these monsoon systems our results suggest that the monsoon climate has already been established in southwest yunnan during the late miocene furthermore our results support that both southeast asian and east asian monsoons co occurred in yunnan during the late miocene c 2010 elsevier b v all rights reserved

prospectivity analysis of orogenic gold deposits in saqez sardasht goldfield zagros orogen iran abstract diverse deposit types or mineral systems form by diverse geological processes so translation of knowledge about the controls of mineralization acquired from the 4d geological modeling into 2d spatial predictor maps is a major challenge for prospectivity analysis in this regard mathematical functions have been used to model the conceptual or perceived spatial relationships between geological variables and targeted type or system of mineralization in this paper due to the different models of spatial relationships between predictors and mineral deposits we investigated the performance of different fuzzification functions to quantify the relationships we demonstrated that various types of relationships between exploration features and a mineralization type sought could be quantified using different fuzzification functions for prospectivity analysis we illustrated the process of the prospectivity analysis by using a data set of orogenic gold deposits in saqez sardasht goldfield iran prospectivity modeling of orogenic gold mineralization in the study area showed that the ne sw trending targets have priority for further prospecting of the deposits

application of mineral equilibria modeling to constrain t and x co2 conditions during the evolution of the magdala gold deposit stawell victoria australia mineral equilibria modeling involving solid solution calculations has been combined with mineral assemblage information from the alteration zones associated with gold mineralization to determine the t and xco2 conditions for the formation of the magdala gold deposit at stawell victoria australia economic gold mineralization is primarily hosted within the stilpnomelane alteration zone of the stawell facies that is adjacent to the magdala basalt evolution of the magdala gold deposit involved at least three fluid infiltration events 1 a co2 bearing fluid during the d2 deformation event produced carbonate spots throughout the chlorite zone 2 a co2 s k bearing fluid accompanied the d3 4ab deformation and produced a muscovite zone and siderite rims on ankerite and 3 a co2 k s au bearing fluid during the d4c deformation event produced the stilpnomelane zone of the stawell facies the proximal and distal alteration zones within the magdala basalt and the main economic gold mineralization mineral equilibria modeling constrains the temperature of formation of the magdala deposit to t 345 390 c at 3kbar substantially lower than indicated by other previous classical thermobarometry methods furthermore this method has allowed the characterization of the mineralizing fluid and constrained its composition to xco2 0 08 at 3kbar the timing and composition of the mineralizing fluids are similar to that of metamorphic fluid generated from devolatilization of a greenstone pile with peak of metamorphism occurring earlier and at deeper levels in the crust

the clay fabric of shales is a strain gauge abstract shales with their large clay fraction are prone to deform in an almost ductile way under tectonic loading here we propose to monitor and quantify the evolution of strained shales clay fabric in the field of illite diagenesis by using magnetic fabric in the footwall of a south pyrenean thrust 281 shales samples have been collected along a 2 km long exceptional exposure the cleavage evolves from pencil structures at 1 km of the thrust to pencil cleavage at 850 m and slaty cleavage at 170 m the average magnetic foliation of illite remains nearly parallel to bedding over a distance of 600 m despite development of pencil cleavage it is at 600 m of the thrust that illite foliation shifts gradually from bedding to cleavage by contrast the magnetic fabric scalar data reflect a more continuous evolution of the deformation the application of a rigid rotation model of the clays allows to quantify the strain magnitude using eigen values of tensor this strain magnitude is consistent with distance to the thrust and conforms favorably with a trishear modelling of this thrust damage we demonstrate therefore that the magnetic fabric of illite rich shales is a strain gauge

lithospheric controls on the formation of provinces hosting giant orogenic gold deposits ages of giant gold systems 500 t gold cluster within well defined periods of lithospheric growth at continental margins and it is the orogen scale processes during these mainly late archaean palaeoproterozoic and phanerozoic times that ultimately determine gold endowment of a province in an orogen a critical factor for giant orogenic gold provinces appears to be thickness of the subcontinental lithospheric mantle sclm beneath a province at the time of gold mineralisation as giant gold deposits are much more likely to develop in orogens with subducted oceanic or thin continental lithosphere a proxy for the latter is a short pre mineralisation crustal history such that thick sclm was not developed before gold deposition in constrast orogens with protracted pre mineralisation crustal histories are more likely to be characterised by a thick sclm that is difficult to delaminate and hence such provinces will normally be poorly endowed the nature of the lithosphere also influences the intrinsic gold concentrations of potential source rocks with back arc basalts transitional basalts and basanites enriched in gold relative to other rock sequences thus segments of orogens with thin lithosphere may enjoy the conjunction of giant scale fluid flux through gold enriched sequences although the nature of the lithosphere plays the crucial role in dictating which orogenic gold provinces will contain one or more giant deposits the precise siting of those giants depends on the critical conjunction of a number of province scale factors such features control plumbing systems traps and seals in tectonically and lithospherically suitable terranes within orogens

the genesis and tectonic control on archaean gold deposits of the western australian shield a metamorphic replacement model abstract gold deposits occur in greenstone belts world wide and contribute to anomalously high gold production from archaean terranes as in other cratons archaean gold mineralization of western australia represents a complex array of deposit styles despite this most deposits are clearly epigenetic and large deposits have a number of features in common including their strong structural controls distinctive wallrock alteration fe sulphide k mica albite ca mg fe carbonates consistent metal associations au ag as sb w b low base metals commonly fe rich host rocks great depth extension and lack of appreciable vertical zonation these shared characteristics combined with their ubiquitous occurrence indicate that archaean gold deposits had a common origin related to the tectonic evolution of greenstone belts auriferous hydrothermal systems were broadly synchronous with regional metamorphism and emplacement of synkinematic granitoids and felsic porphyry intrusions although these gold systems involved low salinity lowdensity reduced near neutral h 2 o co 2 fluids carrying gold as reduced sulphur complexes the origin of the fluids is equivocal most timing evidence and stable isotope data cannot distinguish metamorphic from magmatic granitoid or felsic porphyry orggins but the lack of consistent spatial relationships between specific volumetrically significant intrusive phases and large gold deposits in a number of cratons strongly favours metamorphic derivation of fluids the metamorphic replacement model for gold mineralization involves devolatilization of the lower portions of the greenstone pile with high geothermal gradients inhibiting significant melting co 2 possibly formed by the decarbonation of early alteration related to mantle degassing along crustal scale synbasinal fault zones auriferous fluids were channelled along greenstone scale faults in part developed during reactivation of crustal scale faults in a strike slip regime gold deposition occurred largely under greenschist facies conditions about 300 400 c 1 2 kb in response to decreasing gold solubility with declining temperature however a major control on gold deposition was fluid wallrock interaction many large deposits formed by sulphidation of fe rich host rocks with synchronous deposition of fe sulphides and gold however the variable nature of gold depositing reactions including lowering of fo 2 and ph allowed a multitude of small and some large deposits to form wherever that fluid circulation occurred in consequence several of the relatively small deposits currently worked from open pit are hosted by ultramafic and felsic rocks there are few constraints on the source of components au s k co 2 added to gold deposits but even giant deposits such as the golden mile kalgoorlie could have formed from a realistic greenstone source volume ca 8 8 5 km convective circulation of fluids could have contributed to the generation of high fluid rock ratios on the regional scale the markedly heterogeneous distribution of large gold deposits gold productivity and host rocks to deposits can be accommodated by the metamorphic replacement model the most favourable conditions for development of auriferous hydrothermal systems operated in younger ca 2 7 0 1 ga rift phase greenstones where greatest extension and crustal thinning produced high geothermal gradients crustal scale synbasinal faults and rapid extrusion and burial of volcanics including abundant komatiites iron rich tholeiitic basalts and dolerites were preferred host rocks for large gold deposits the least favourable conditions existed in older ca 3 5 3 4 ga platformphase greenstones where gentle sagging on submerged continental crust produced eruption of mainly mafic volcanics with few komatiites commonly in very shallow water environments this allowed intense synvolcanic alteration of both gold source rocks and potential host rocks the generally smaller gold deposits formed mainly in ultramafic or greywacke hosts younger ca 3 0 ga platform phase greenstones appear intermediate in nature but unlike other greenstones have significant epigenetic gold deposits in originally oxide facies bif which were deposited on relatively deep water platforms similar controls appear to exist on a world scale with gold mineralization peaking at ca 2 7 0 1 ga in response to development of major rift zones in thickened relatively mature continental crust interestingly the giant witwatersrand goldfield formed at about the same time

orogenic gold mineral systems of the western lachlan orogen victoria and the hodgkinson province queensland crustal metal sources and cryptic zones of regional fluid flow abstract orogenic gold mineral systems in the western lachlan orogen victoria and the hodgkinson province queensland produced gold provinces characterised by vastly different scales of gold endowment and strongly uneven distribution of gold mineralisation within each province the volume of hydrous pyrite bearing rocks undergoing metamorphic devolatilisation during thermo tectonic events driving orogenic gold mineral systems represents a fundamental first order constraint on the total gold endowment and its broad spatial distribution both between and within the provinces most of the largest gold deposits in both regions occur in linear richly endowed metallogenic zones oblique to the dominant regional structures and related to deep crustal domain boundaries these boundaries with only subtle surface expressions were the major regional structural controls which promoted focused near vertical flow of mineralising metamorphic fluids above the outer margins of cratonic blocks in the lower crust recognised major faults represented only more local scale and often indirect controls on the focused fluid flow particularly effective above the deep cratonic block boundaries overlain by relatively thick crustal source rocks

porphyry copper deposit density estimating numbers of undiscovered mineral deposits has been a source of unease among economic geologists yet is a fundamental task in considering future supplies of resources estimates can be based on frequencies of deposits per unit of permissive area in control areas around the world in the same way that grade and tonnage frequencies are models of sizes and qualities of undiscovered deposits to prevent biased estimates it is critical that for a particular deposit type these deposit density models be internally consistent with descriptive and grade and tonnage models of the same type in this analysis only deposits and prospects that are likely to be included in future grade and tonnage models are employed and deposits that have mineralization or alteration separated by less than an arbitrary but consistent distance 2 km for porphyry copper deposits are combined into one deposit only 286 deposits and prospects that have more than half of the deposit not covered by postmineral rocks sediments or ice were counted nineteen control areas were selected and outlined along borders of hosting magmatic arc terranes based on three main features 1 extensive exploration for porphyry copper deposits 2 definable geologic settings of the porphyry copper deposits in island and continental volcanic arc subduction boundary zones and 3 diversity of epochs of porphyry copper deposit formation porphyry copper deposit densities vary from 2 to 128 deposits per 100 000 km2 of exposed permissive rock and the density histogram is skewed to high values ninety percent of the control areas have densities of four or more deposits 50 percent have densities of 15 or more deposits and 10 percent have densities of 35 or more deposits per 100 000 km2 deposit density is not related to age or depth of emplacement porphyry copper deposit density is inversely related to the exposed area of permissive rock the linear regression line and confidence limits constructed with the 19 control areas can be used to estimate the number of undiscovered deposits given the size of a permissive area in an example of the use of the equations we estimate a 90 percent chance of at least four a 50 percent chance of at least 11 and a 10 percent chance of at least 34 undiscovered porphyry copper deposits in the exposed parts of the andean belt of antarctica which has no known deposits in a permissive area of about 76 000 km2 measures of densities of deposits presented here allow rather simple yet robust estimation of the number of undiscovered porphyry copper deposits in exposed or covered permissive terranes

plio pleistocene floras of the vildstejn formation in the cheb basin czech republic a floristic and palaeoenvironmental review abstract plant fossil assemblages foliage fruits and seeds pollen wood from the pliocene and early pleistocene deposits in w bohemia the vildstejn formation of the cheb basin tachov cheb doma lice graben are newly analysed using several palaeoenvironmental methods with the aim to reconstruct palaeovegetation and palaeoclimatic changes floras of four subsequent stratigraphic levels show a decrease of exotic elements in the pliocene and a massive immigration of boreal elements in the early pleistocene vegetation changes start with broad leaved deciduous and mixed mesophytic forests and continue towards light forests of the mentioned types in areas of zonal to extrazonal habitats this vegetational change is characterised by an immigration of dry herbaceous and sclerophyllous elements wetland communities from higher positions in the profiles stepwise loose exotic components and point to cool temperate conditions similar to the present conditions palaeoclimatic signals show warmer and more humid conditions for the pliocene levels about 15 c of mean annual temperature 5 c of mean temperature of the coldest month and 25 c of mean temperature of the warmest month more than 900 mm of mean annual precipitation early pleistocene proxy data indicate the beginning of a cooler phase at the plio pleistocene boundary about 7 c of mean annual temperature and decreasing trend of precipitation but conditions not colder than those of the present day in the nw part of the bohemian massif

flexural slip generated bedding parallel veins from central victoria australia abstract thin continuous laminated bedding parallel quartz veins bpvs with slip striated and fibred vein walls occur within slates or at their contact with sandstones on the limbs of chevron folds in the bendigo castlemaine goldfields southeastern australia two microstructural types of bpv i and ii have been previously recognized and are confirmed in this study both types are concluded to have formed during and or after crenulation cleavage the first tectonic axial planar structure in the wallrock slates and during flexural slip folding type i bpvs consist of syntaxial phyllosilicate inclusion trails parallel to bedding enclosing inclined inclusion bands the latter formed by detachment of wallrock phyllosilicate particles from the walls of pressure solution segmented discordant tension veins type i bpvs are formed by bedding parallel shear and grow in width by propagation of the discordant veins into the bpv walls type ii veins are composed of quartz bands separated by wallrock slate seams which have split away from the vein wall during dilatant shear opening they incorporate numerous torn apart fragments of crenulated wallrock slate type i bpv inclusion band average spacing of 0 5 mm probably represents the magnitude of slip increments during stick slip flexural slip folding activity

intracrustal detachments and implications for crustal evolution within the lachlan fold belt southeastern australia seismic reflection profiling in the southern lachlan fold belt australia indicates geometrically complex mid to lower crustal detachments possibly associated with crustal thickening by tectonic underplating of collided microplates and or oceanic plateaus low angle detachments either intersect or sole into the crust mantle boundary forming a crustal stacking wedge typical of lithospheric or a type subduction upper crustal reflections show that major moderately to steeply dipping reverse faults exposed at the surface flatten with depth and have listric form the chevron folded quartz rich turbidite sequence of the lachlan fold belt is therefore allochthonous with respect to the lower crust like the northern appalachian maritimes the lachlan fold belt has a composite crust with diverse lower crustal blocks overlain by allochthonous imbricated terranes of the surface rocks

crustal scale fluid pathways and source rocks in the victorian gold province australia insights from deep seismic reflection profiles deep seismic reflection data collected across the western lachlan orogen of southeast australia have provided important insights into crustal scale fluid pathways and possible source rocks in one of the richest orogenic gold provinces in the world the profiles span three of the most productive structural zones in victoria the stawell bendigo and melbourne zones zone scale variations in the age and style of gold deposits correspond with differences in crustal structure and composition the bilateral distribution of gold production in the stawell and bendigo zones is related to the v shaped crustal scale geometry of the two zones in cross section major first order faults like the east dipping moyston fault and a set of west dipping listric faults within the bendigo zone were probably major fluid conduits in the lower to middle crust during gold mineralization first order faults in the stawell and bendigo structural zones appear to have accommodated large scale thickening down to the lower crust the faults converge in a region beneath the western bendigo zone where a thick section of mafic volcanic rocks and lesser sedimentary rocks are identified as a likely common source of gold bearing fluid that was largely generated by late ordovician to early silurian metamorphism the areas with the greatest gold endowment lie above lower crustal regions that have preserved the thickest succession of fertile mafic igneous rocks up to about 25 km thick they also correspond to a region of thin or absent precambrian lithosphere mafic rocks in the stawell zone and far western bendigo zone were probably partly consumed by cambrian west dipping subduction similar rocks in the rest of the bendigo zone lay outside the influence of cambrian subduction accretion and were deformed later probably beginning in the late ordovician early silurian benambran orogeny during crustal scale imbrication this imbrication preserved much of the mafic rocks to form the lower to middle crust first order listric faults in the bendigo zone are interpreted as major controls on the locations of goldfields even though they are largely unmineralized near the present surface the shallow dipping segments of first order listric faults were favorably oriented for reactivation at the time of gold mineralization and acted as major fluid conduits in the lower to middle crust in contrast the upper steeply dipping segments of first order listric faults were unfavorably oriented for reactivation and were poor fluid conduits the seismic data show that the transition from predominantly shallow to steeply dipping fault segments occurs in the middle to upper crust near the boundary between thick imbricated metavolcanic rocks that lie immediately below 6 to 15 km of folded metasedimentary rocks this transition may have coincided with fluid escape zones that aided the transfer of permeability away from first order faults and into the overlying fold dominated turbidites this transfer of permeability was enhanced by the growth of subvertical fold related fault and fracture meshes in the upper crustal turbidites the fault and fracture meshes consisted of bedding parallel faults limb thrusts and tension vein arrays that developed along fold hinges in the bendigo zone individual fold hinges and regional fold culminations were important controls on the distribution of fluid flow fluid flow was partly syndeformational but overlapped into the immediate postdeformational period of the benambran orogeny later reactivation of first order faults in the late silurian to early devonian and again in the late devonian led to further although less important mineralizing events as fluids exploited the preexisting fault architecture deeply penetrating north dipping listric faults in the less gold rich melbourne zone cut into inferred proterozoic basement and may have been fluid conduits during a late devonian mineralizing event

re os dating of sulfides associated with gold mineralization in central victoria australia we report re os isotope ages that are the first for sulfides closely associated with gold mineralization at the bendigo and maldon goldfields in central victoria two arsenopyrite samples from bendigo contain 11 ppb re and 0 08 ppb highly radiogenic os llhr samples stein et al 2000 and have model ages of 444 7 and 447 7 ma with a mean model age of 446 5 ma a five point isochron based on these arsenopyrite analyses plus three pyrite analyses including one replicate gives an age of 438 6 ma molybdenite associated with au te cu and sb mineralization at maldon gives an re os age of 376 2 ma similar to the age of the nearby har court granite these results support previous 40 ar 39 ar data indicating that initial emplacement of gold mineralization in central victoria occurred in the late ordovician during the earliest stages of accretionary development of the southern lachlan fold belt the molybdenite data are also consistent with the mobilization and or introduction of gold during late devonian magmatism

orogenic disseminated gold in phanerozoic fold belts examples from victoria australia and elsewhere abstract orogenic gold mineralisation in the lachlan orogen of southeastern australia and in other phanerozoic fold belts has generally been assumed to be confined entirely to quartz veins however an improved understanding of the tectonic structural and geochronological framework in which these occurrences form and recent advances towards the extent of wallrock alteration around these veins cast doubt on the validity of this deeply entrenched lode gold paradigm ore grade orogenic disseminated gold mineralisation has been recognised in a number of fold belts that are known to host significant orogenic lode gold deposits lachlan orogen australia buller terrane and otago schist new zealand meguma terrane canada tien shan mountains in uzbekistan and kyrgyzstan yana kolyma province baikal verhoyansk and allakh yun fold belts in north central mongolia and far east russia disseminated mineralisation in these collisional belts is invariably hosted by pervasively altered greenschist to subgreenschist facies rocks these occurrences also share a number of characteristics with some carlin type gold deposits in the great basin of western north america e g getchell regarding structural relationships fluid composition mineral paragenesis and a common association of carbonaceous matter with mineralisation features of alteration physico chemical characteristics of the ore bearing fluids and strong structural control in all of the studied occurrences point to a close genetic association with lode gold mineralisation the two styles are considered to represent end members of a crustal continuum of orogenic gold emplacement in phanerozoic fold belts with disseminated mineralisation more likely to develop at shallower levels and within more permeable units during the waning stages of uplift and exhumation these conditions facilitate ground preparation via brittle fracturing and the development of intricate stockwork systems efficient gold segregation from bisulphide complexes is largely controlled by fluid mixing of an evolved metamorphic fluid with either more oxidised ascending fluids or meteoric fluids and accelerated by the presence of carbonaceous matter at the site of deposition

paleoclimatic estimation reveals a weak winter monsoon in southwestern china during the late miocene evidence from plant macrofossils the late miocene xianfeng flora of yunnan province southwestern china was chosen to reconstruct the paleoclimate and the intensity of the asian monsoon three available quantitative climate reconstruction methods from fossil plants i e leaf margin analysis lma the climate leaf analysis multivariate program clamp and the coexistence approach ca were used in this study mats mean annual temperatures resulting from these three approaches i e lma 17 2 2 38 degrees c clamp 15 43 1 25 degrees c ca 17 2 21 7 degrees c appear to have been higher than the present 14 9 degrees c suggesting a much warmer climate in the late miocene both the growing season precipitation gsp from clamp 1908 7 217 7 mm and mean annual precipitation map from ca 1206 0 1613 0 mm estimates are higher than modern values 1003 2 mm gsp and 1038 mm map respectively indicating a more humid climate during the late miocene by comparing these with climates reconstructed from neighboring late miocene floras we conclude that the general late miocene climate appears warmer and more humid than present conditions in southwestern china furthermore the evident differences in estimated monthly temperatures between the summer and winter and precipitations between the humid and dry seasons indicate the existence of seasonality though not as strong as that of today difference in precipitation of dry season indicates a marked strengthening in the winter monsoon since the late miocene a new monsoon intensity index has also been defined based on precipitation seasonality to investigate the intensity of the asian monsoon c 2012 elsevier b v all rights reserved

high resolution analysis of upper miocene lake deposits evidence for the influence of gleissberg band solar forcing article i nfo a high resolution multi proxy analysis was conducted on a 1 5 m long core of tortonian age 10 5 ma late miocene from austria europe the lake sediments were studied with a 1 cm resolution to detect all small scale variations based on palynomorphs pollen and dinoflagellate cysts ostracod abundance geochemistry carbon and sulfur and geophysics magnetic susceptibility and natural gamma radiation based on an already established age model for a longer interval of the same core this sequence can be limited to approx two millennia of late miocene time with a resolution of 13 7 years per sample the previous study documented the presence of solar forcing which was verified within various proxies on this 1 5 m core by a combination of redfit spectra and gaussian filters significant repetitive signals ranged in two discrete intervals corresponding roughly to 55 82 and 110 123 years fitting well within the lower and upper gleissberg cycle ranges based on these results the environmental changes along the 2000 year late miocene sequence are discussed no major ecological turnovers are expected in this very short interval nonetheless even within this brief time span dinoflagellates document rapid changes between oligotrophic and eutrophic conditions which are frequently coupled with lake stratification and dysoxic bottom waters these phases prevented ostracods and molluscs from settling and promoted the activity of sulfur bacteria the pollen record indicates rather stable wetland vegetation with a forested hinterland shifts in the pollen spectra can be mainly attributed to variations in transport mechanisms these are represented by a few phases of fluvial input but mainly by changes in wind intensity and probably also wind direction such influence is most likely caused by solar cycles leading to a change in source area for the input into the lake furthermore these solar induced variations seem to be modulated by longer solar cycles the filtered data display comparable patterns and modulations which seem to be forced by the 1000 year and 1500 year cycles the 1000 year cycle modulated especially the lake surface proxies whereas the 1500 year cycle is mainly reflected in hinterland proxies indicating strong influence on transport mechanisms

late structural control of mesothermal vein hosted gold deposits in central victoria australia mineralization mechanisms and exploration potential abstract comparison of the structural relationships between five gold deposits in ordovician rocks of the central victorian slate belt reveals a similar history and structural control of gold mineralization large quartz veins spatially associated with gold mineralization such as the famous saddle reefs of bendigo formed during the second deformation earlier than the gold mineralization itself where they were overprinted by the effects of the fourth deformation they provided structural sites for gold deposition on their boundaries with country rock where brecciation jostling and fracture were favoured access of fluids resulting from metamorphism and deformation to the brecciated fractured and jostled blocks of country rock created conditions suitable for the precipitation of gold through a sequence of alteration replacement and infill the dominant structural relationships that resulted in the generation of these sites were a the high angle of the axial plane of the fourth deformation to earlier structures and b the presence during mineralization of large pre existing quartz veins that acted as structural discontinuities on which brecciation could occur these factors allow a predictive capacity for exploration in the region

a fluid inclusion study of the fosterville mine a turbidite hosted gold field in the western lachlan fold belt victoria australia abstract gold mineralisation at fosterville occurs in association with disseminated arsenopyrite and pyrite adjacent to a complex series of quartz carbonate veins along two nnw trending fault zones quartz carbonate veins which have formed in dilational fractures within the sulphide ore zone have 18 o values between 16 0 and 17 6 and contain the following types of fluid inclusions type ia two phase liquid rich inclusions with less than 10 vol vapour and no detectable gases type ib two phase inclusions with approximately 10 vol co 2 rich vapour type ii co 2 bearing inclusions with 30 vol vapour and type iii liquid h 2 o and liquid plus vapour co 2 inclusions with variable h 2 o co 2 ratios raman microprobe analysis showed that types ib ii and iii contain co 2 with variable amounts of n 2 and ch 4 in some inclusions type 1a aqueous inclusions from stage 4 of the paragenesis have salinities ranging from 5 to 7 wt nacl equivalent whereas the co 2 bearing inclusions in the same stage have average salinities around 3 5 4 0 wt nacl equivalent the co 2 bearing inclusions exhibited two different types of homogenisation behaviour vapour rich type ii and iii inclusions either homogenised to vapour or showed near critical behaviour by gradual fading of the meniscus with homogenisation temperatures from 234 to 384 c and a mode at 270 c liquid rich co 2 bearing inclusions homogenised to the liquid phase with a bimodal distribution the majority of inclusions homogenised between 243 c and 314 c with a mode around 270 c but a secondary mode occurs around 180 c this mode corresponds fairly closely to the mode observed for the aqueous type 1a inclusions at 170 c the variable salinities coexisting liquid and vapour rich inclusions and the overlap of the homogenisation temperatures suggest that phase separation has occurred during vein formation and the resulting depth of mineralisation is estimated to be between 2 6 and 5 7 km gold precipitation resulted from the partitioning of h 2 s into the vapour phase during fluid unmixing which was enhanced both by the decreasing pressure as fluid flowed from the faults and veins into the host rocks and by the addition of n 2 and ch 4 comparisons with available fluid inclusion data for the western lachlan fold belt indicates that the fosterville gold field formed at lower temperatures and at a higher crustal level than the quartz reef style of gold deposits in the bendigo ballarat zone the fluids at fosterville also contain greater amounts of n 2 and ch 4 suggesting that the mineralising fluids penetrated further into the host rocks and reacted either directly with carbonaceous matter or with reduced fluids contained within the host rocks

palaeoclimatic and palaeoenvironmental interpretations of the late oligocene late miocene early pliocene in the cankiri corum basin abstract palaeoclimatic and palaeoenvironmental interpretations are reconstructed from the sedimentary sequences of the late oligocene and miocene pliocene boundary in the cankiri corum basin based on evidence obtained from palynofloras and ostracod and mammal faunas information on the main role of mixed mesophytic and broad leaved evergreen forests was obtained from the late oligocene data from the guvendik formation the pollen records of the formation showed a greater proportion of the hygrophytic forest communities thermophilic taxa and the taxonomic diversity of these forest communities developed mainly under dry subtropical climate conditions palynofloras and ostracods of the latest miocene and earliest pliocene were determined from coal bearing sediments of the akasdagi formation in central turkey the latest miocene palynoflora was represented by low diversity and abundance of spores and pollen and it was characterized by mainly grassland species the earliest pliocene palynoflora differs from that of the latest miocene through the presence of abundant and diverse palynomorphs this palaeovegetation diversification from the latest miocene to earliest pliocene can be related to changes in temperature and precipitation in the southern part of the cankiri corum basin the identified ostracods palynomorphs indicative of brackish environments and a high abundance of gypsum crystals observed from the lower part of the akkasdagi formation suggest brackish conditions during the latest miocene palynological evidence and results using the coexistence approach indicate that climate evolution in central turkey during this period can be referred to ongoing tectonic activity in this area and global climate change during the neogene

wallrock alteration associated with turbidite hosted gold deposits examples from the palaeozoic lachlan fold belt in central victoria australia abstract the study of wallrock alteration phenomena around slate belt hosted gold deposits can provide valuable information regarding the physico chemical conditions of the ore bearing fluids and the timing relationships between deformation peak metamorphism granitoid emplacement and mineralisation thus studying the processes involved in the interaction of the hydrothermal fluids with the host rock is critical in order to constrain genetic models and ultimately as a tool for exploration largely due to the characteristics of the host rocks turbidite hosted mesothermal gold deposits were historically believed to lack such diagnostic alteration haloes and their study has long been neglected however recent studies in the palaeozoic lachlan fold belt in southeastern australia and in similar tectonic settings elsewhere have demonstrated that alteration around many of these deposits is more widespread and pervasive than previously thought a review of existing information and new data strongly support the viability of studying hydrothermal alteration as a guide to turbidite hosted mineralisation and as an indicator of the character of the solutions associated with ore deposition characteristically the auriferous reef structures are surrounded by broad bleached zones while disseminations of carbonate spots pyrite and arsenopyrite porphyroblasts are the most obvious features of alteration depending on parameters such as fault geometry fluid pressure and reactivity and permeability of the host rocks these disseminations can occur up to a kilometre away from the auriferous structures sericitisation and carbonatisation are commonly discernible within 3 to 10 m wide haloes wallrock alteration chemistry of turbidite hosted gold deposits in the lachlan fold belt shows consistent enrichments of k2o co2 s and as and the anomalous values of these elements also provide the most useful dispersion haloes for turbidite hosted gold exploration due to both their regularity and extent

entering an immature exploration search space assessment of the potential orogenic gold endowment of the sandstone greenstone belt yilgarn craton by application of zipf s law and comparison with the adjacent agnew goldfield abstract the sandstone greenstone belt is an exploration immature regolith covered approximately 1000 sq km belt in the southern cross domain of the yilgarn craton in order to estimate potential endowment historical gold production and deposit resource estimates are required to be quantitatively analysed for calculation of natural and residual gold endowment the total residual gold endowment within the oxide zone of the sandstone greenstone belt is estimated by application of a zipf s law statistical assessment to be 2 3 moz this mineralisation is most likely contained in extensions of known deposits and several undiscovered deposits the fresh rock of the sandstone greenstone belt remains poorly explored however a conceptual endowment estimate can be made based on a minerals system comparison between the exploration immature sandstone greenstone belt and the well explored geologically similar agnew greenstone belt 100 km to the east it is possible that natural endowment at sandstone could total 21 3 moz with nine undiscovered deposits of 0 5 moz application of such a minerals system integrated endowment assessment represents an effective motivator to embark on a well resourced gold exploration campaign in the sandstone greenstone belt a currently immature exploration search space

stress controls on intrusion related gold lodes wonga gold mine stawell western lachlan fold belt southeastern australia the wonga gold lodes 300 000 oz au in the victorian gold fields of eastern australia formed at a depth of less than 7 km within the seismogenic zone the wonga gold deposit is hosted by mudstone dominant lithofacies that define the core of the regional synform these are underlain by sandstone dominant lithofacies that are interlayered with mafic schist the lodes occur within the contact aureole of a late stage granitic body that intrudes an earlier phase of the fractionated pluton in contrast to the nearby 440 ma magdala orogenic gold lodes 5 moz au this smaller deposit formed at ca 400 ma and has been classified as intrusion related the orogenic and intrusion related gold deposits formed at different stages in the structural and magmatic evolution of the fold belt and at different crustal levels compared to the magdala lodes the wonga lodes have a close temporal and spatial relationship with the intrusive rocks and a distinct structural style and mineralogy including acicular arsenopyrite stibnite gold telluride alloys bismuth silver and late stage molybdenite the wonga lodes formed between two distinct phases of regional faulting and the kinematics of the mineralized structures cannot be correlated with any preserved far field regional paleostresses instead they are inferred to reflect the local state of stress at the point that magmatic related fluid overpressure occurred pervasive fluid overpressure drove deformation across a broad zone producing massive mineralized quartz vein structures that included angular clasts of wall rock a discrete overpressure event is suggested rather than repeated crack seal behavior the lodes represent an early stage in the development of a fault zone characterized by a series of discontinuous discrete shear failures the geometry of the lodes is strongly dependent on structural position and rheology northeast dipping preexisting weaknesses such as dike margins and variably developed crenulation cleavages produced localized shear failure defined by dextral reverse slip structures the hanging wall structures 30 to 60 se dipping extension veins and extensional shear veins the link structures diverge from these creating en echelon lode geometries there is a sudden change over the top of a regional plunge reversal defined by the dominant fold axes from shear failure the hanging wall structures to extensional shear and then extensional failure the links this occurs along strike in the same structural corridor and within the same stratigraphic unit the explicit finite difference code flac was used to model the local state of stress at the point where an influx of magmatic fluids raised the pore fluid pressure the model predicts that a zone of slightly lower differential stress was associated with the plunge reversal and this variation in differential stress is interpreted to have caused the drastic change in lode style the modeling highlights that only subtle differences in the elastic moduli of the rocks are required to produce the observed stress geometry

structural and geochemical controls on the development of turbidite hosted gold quartz vein deposits wattle gully mine central victoria australia gold quartz vein deposits in the wattle gully mine arefault related structures developed in a low grade metamorphosed ordovician quartz rich flysch sequence the major mineralization is associated with a high angle reverse fault wattle gully fault that has a maximum displacement of 40 m over 10 6 metric tons t of vein quartz averaging 10 5 g t au occur within a dilatant jog in this structure fold geometry has controlled fault geometry and resulted in the localization of the jog segment where the wattle gully fault traverses an east dipping fold limb to link two more steeply dipping bedding parallel fault sediments on adjacent west dipping fold limbs gold mineralization is also associated with several minor east clipping reverse faults and a bedding parallel fault whose development is related to flexural slip during fold tightening mineralization occurs within fault fill veins and extension veins adjacent to faults the geometry and internal structures of veins indicate that vein growth has been controlled by repeated fluctuations in fluid pressure and shear stress associated with fault valve behavior vein mineralogy is dominated by quartz with minor carbonates chlorite white mica albite and apatite arsenopyrite and pyrite are the major sulfide phases but sphalerite galena chalcopyrite and pyrrhotite are also present the highest au grades tend to be localised in vein systems that are in proximity to carbonaceous slates wall rock alteration is minor and restricted mainly to narrow zones adjacent to major vein systems sulfur isotope fractionation between galena and sphalerite indicates mineralization occurred at temperatures around 300 degrees c the delta 34 s compositions of pyrite and arsenopyrite are nearly uniform throughout the mine 1 5 2 8 but are generally not in equilibrium with the delta 34 s values of associated base metal sulfides 0 7 5 3 the delta 18 o values for vein quartz vary between 15 6 and 18 0 per mil and correspond to delta 18 o values