gold bearing mesothermal veins from the gubong mine cheongyang gold district republic of korea fluid inclusion and stable isotope studies the gubong deposit consists of five massive gold bearing mesothermal quartz veins that fill fractures oriented northeast and northwest along fault shear zones over an area of 14 km2 in precambrian metasedimentary rocks of the gyeonggi massif the veins are divided into three groups based on their orientation and location they have a ribbon texture that is interpreted to result from repeated hydraulic fracturing events mineral deposition was associated with hydrothermal fluid overpressuring within and below the active fault shear zones the vein mineralogy and paragenesis of the veins allow two separate discrete mineralization episodes to be recognized separated by a major faulting event the ore minerals are contained within quartz and calcite associated with fracturing and healing of veins that occurred during both mineralization episodes wall rock alteration minerals during stage i the main ore stage include sericite chlorite and minor pyrite and carbonates sulfide minerals deposited along with electrum during this stage include arsenopyrite pyrite pyrrhotite sphalerite marcasite chalcopyrite galena and argentite electrum also was deposited during stage ii mineralization in the one group of veins along with pyrite sphalerite chalcopyrite and galena but the second stage of deposition in other veins was barren petrographic examination of textural relationships among sulfides fluid inclusions microfracturing and quartz shows chronological and genetic relationships between gold deposition and fluid entrapment systematic studies of fluid inclusions in stage i vein indicate two contrasting events a relatively high temperature 203 432 c and pressure 943 2 098 bars event related to early sulfide deposition and associated with h2o co2 ch4 nacl n2 fluids less than about 13 4 wt nacl and a lower temperature 202 399 c and pressure 670 850 bars late sulfide depositional event involving h2o nacl fluids 3 9 17 3 wt nacl the h2o nacl fluid involved in ore related stage ii mineralization had a salinity of 0 4 to 4 2 wt percent nacl and a homogenization temperature of 201 to 378 c the calculated sulfur isotope compositions of hydrothermal fluids from the stage i veins 34sh2s 3 5 10 5 indicate that ore sulfur was derived mainly from a magmatic source but also in part from sulfur contained in the host rocks the calculated and measured oxygen and hydrogen isotope compositions of the ore forming fluids stage i 18oh2o 1 1 9 0 d 92 to 21 stage ii 18oh2o 0 1 to 0 3 d 95 to 93 indicate that the fluids were derived from magmatic and or deep seated metasedimentary rocks stage i and evolved by mixing with local meteoric water stage ii by limited water rock exchange and by degassing during mineralization in uplift zones the h2o nacl fluids involved in the stage i development of these veins represent fluids that evolved either through unmixing of h2o co2 ch4 nacl n2 fluids following a decrease in fluid pressure or through mixing with deeply circulating meteoric waters possibly as a result of uplift and or unloading during mineralization the h2o nacl fluid involved in stage ii was derived from meteoric water early deposition of gold in stage i was caused by a decrease in sulfur fugacity h2s loss that accompanied the immiscible separation of carbonic vapor from h2o co2 ch4 nacl n2 fluids gold in late stage i and stage ii veins was precipitated from h2o nacl fluids by cooling and by dilution caused by mixing with meteoric water

geochronology and geochemistry of the frieda river prospect area papua new guinea the frieda river prospect is located between the frieda and lagaip fault zones two major structural features of the new guinea mobile belt in the west sepik district papua new guinea the prospect can be subdivided into three spatially and geologically different areas frieda complex mianmin area and nena diorite area the frieda complex is the remnant volcanic edifice of an island stratovolcano interstratified in the mid miocene wogamush formation intrusive and volcanic units in the complex are texturally similar andesitic hornblende plagioclase porphyries and are probably comagmatic pyritic replacement copper gold and porphyry copper deposits are associated with early and late phases respectively of extensive district scale advanced argillic alteration along the central axis of the frieda complex the mianmin area is a separate unmineralized volcanic center that contains igneous rocks similar to those of the frieda complex the nena diorite a composite holocrystalline intermediate to mafic body intrudes upper cretaceous to eocene age basement rocks it is located north of and separated from the frieda complex by the frieda fault igneous activity in the frieda river prospect extended over an interval of at least 4 m y on the basis of field relations and k ar ages this igneous activity is subdivided into early intrusion 17 3 to 16 8 m y ago main intrusion 16 3 to 13 1 m y ago and late alteration about 12 8 to 11 2 m y ago events k ar ages on alunite appear to be too young to be those of formation of this mineral and the oldest 13 0 or 0 4 m y is interpreted as a minimum age for the nena pyritic replacement copper gold deposit geothermal activity which caused district scale alteration extended from earlier than 14 0 or 0 4 m y until about 11 2 or 0 2 m y ago the discordance of about 2 m y between k ar ages of coexisting hornblende and biotite in two diorites is thought to register the cooling history of the hydrothermal system a k ar age of 13 6 or 0 4 m y was obtained on hornblende from a sample of horse microdiorite regarded as the progenitor of porphyry copper mineralization this age is interpreted as near that of emplacement and provides an older limit for the age of vein controlled transitional alteration associated with most porphyry copper mineralization the primary biotite apparent k ar age of 11 5 or 0 2 m y from the same sample is accepted as a younger limit for the age of porphyry copper mineralization k ar ages from the mianmin area and the nena diorite area are very similar to those found for dioritic intrusions in the frieda complex intrusive and volcanic rocks of the frieda river prospect exhibit limited compositional variation they are all of andesitic composition and belong to a normal k calc alkaline suite the three geologically distinct areas of the prospect are distinguishable on the basis of rock and mineral chemical differences textural and chemical features of the freida complex and mianmin area igneous rocks are compatible with much of their diversity in lithology and dispersion in chemistry being due to their representing cumulate melt mixtures they are thought to have crystallized from hot 900 degrees c oxidized magmas which were emplaced at a shallow level in the crust p total

magnetic felsic intrusions associated with canadian archean gold deposits felsic intrusions spatially and temporally associated with archean au deposits in the superior province of the canadian shield are magnetic due to high magnetite content in comparison to felsic igneous rocks in most of the archean terrain examples are found in au camps of hemlo red lake harker holloway mishibishu lake wawa missanabie geraldton matachewan and bouquet east cadillac these archean intrusions are comparable with phanerozoic magnetite series plutons accompanying metallic mineralization and magnetiterich intrusions hosting au rich porphyry deposits the evidence shows a distinct tectonic setting for the gold mineralization involving the generation of the particular magmas the association of the two indicates either the derivation of the ore constituents from the intrusions or the emplacement of the magmas along dilation zones which also provided fluid flow from depth the identification of magnetite rich felsic intrusions may aid in targeting favorable exploration areas for archean au deposits

the role of magmatic sulfides and mafic alkaline magmas in the bingham and tintic mining districts utah this paper reports the existence of abundant magmatic sulfides in introduction latite lava vitrophyres and vent facies dikes from the bingham and the eruption of sulfur rich magmas from el chichon tintic districts in central utah these dikes and flows appear to luhr et al 1984 and mt pinatubo westrich gerlach be comagmatic with the ore related monzonite intrusions in addition 1992 in recent years has attracted attention to the limited analytical data suggest that the magmatic sulfides contain most of solubility of sulfur in intermediate magmas and the factors the cu and ag present in the latites magmatic sulfides are preserved potentially responsible for the formation of magmatic only in the least oxidized and least degassed lavas and vitrophyres sulfides and anhydrite however the occurrence of magpetrography of comagmatic dikes and intrusions suggests that matic sulfides in intermediate magmas is not universal resorption and oxidation s degassing of the globules may make many volcanic suites appear to be sulfide unsaturated the metal content available to a magmatic ore fluid minette and inasmuch as magmatic sulfides may sequester chalcophile shoshonite lavas occur in subordinate amounts in the latitic volcanic metals what would their presence signify in magmatic fields associated with latite monzonite intrusions and hydrothermal systems that formed porphyry cu and mesothermal vein ore deposits of the tintic ag pb zn cu au and bingham deposits do they sequester a significant portion of the porphyry cu au mo districts utah the ages chemical and magmatic cu pb zn ag and au thereby restricting modal compositions and field relations of the mafic alkaline lavas metal availability of subsequent ore forming fluids suggest that such magmas mixed and fractionated at shallow crustal we have examined the volcanic rocks from the tintic levels to form the ore related latites and monzonites the unaltered and bingham mining districts fig 1 utah and found mafic alkaline lavas in these districts are some of the most cu rich that almost all of the volcanic units contain magmatic lavas in the great basin province sulfides some quenched dikes and intrusion margins also have preserved magmatic sulfides comparable with those in the volcanic rocks several lines of evidence indicate that the volcanic and intrusive rocks are comagmatic keith et al 1989 1991 waite 1996 the tintic district and east tintic sub district in utah have recorded over

crustal evolution of archean rocks in the kakagi lake area wabigoon subprovince ontario as interpreted from high precision u pb geochronology the evolution of the archean volcanic plutonic complex in the kakagi lake area occurred during a time interval of ca 32 ma the earliest age is from analysis of zircon and baddeleyite in a gabbro intruding the lowermost katimiagamak volcanic group an age of 2723 2 1 8 ma on a tonalite gneiss from the interior of the underlying sabaskong batholith is indistinguishable from a previously dated massive border phase of the batholith and shows no evidence for inheritance from an older sialic component an early tonalite phase from the adjacent aulneau batholith is dated at and the latest granodiorite phase is dated at this defines a time span of about 7 ma for intrusion of the bulk of the batholith and indicates that previously dated felsic volcanism from the uppermost sequence above the kakagi lake volcanic group is coeval with late plutonic activity in the aulneau batholith the end of regional deformation in the area is given by the ages of two late tectonic intrusions the heronry lake pluton and

a tale of two plutons petrographic and mineralogic constraints on the petrogenesis of the red lake and eagle peak plutons central sierra nevada california the red lake and eagle peak plutons are similar in age k ar 87 89 m y and range in composition from granodiorite to granite the red lake pluton is equigranular has a locally greisened marginal zone and shows only minor mineralogical and chemical zoning whereas the eagle peak pluton is mineralogically compositionally and texturally zoned with an equigranular margin and a porphyritic core modal and normative trends within each pluton are consistent with separation of plagioclase and mafic minerals leading to a residual liquid enriched in quartz and alkali feldspar the formation of the prominent alkali feldspar megacrysts in the eagle peak core was promoted by plagioclase separation h 2 o undersaturation and a slower cooling rate relative to the red lake magma early loss of volatiles and a resulting increase in magma melt crystals viscosity inhibited crystal segregation within the red lake pluton and prevented the development of zoning late stage aplites associated with both plutons f

paleomagnetism of the red lake greenstone belt northwestern ontario possible evidence for the timing of gold mineralization we report paleomagnetic results from 1 largely unaltered batholiths and 2 sheared and altered units in the archean red lake greenstone belt a major gold producing region in the uchi subprovince of northwestern ontario group 1 includes the hammell lake killala baird trout lake and little vermilion lake batholiths which were intruded between 2730 and 2700 ma ago u pb zircon group 2 includes the howey diorite the dome stock and dikes and andesites from the dickenson mine these units from the mineralized deformation zones dzs between the batholiths were sheared and hydrothermally altered in the same event that caused gold mineralization in supracrustal units the batholiths carry a stable reversed remanence rlr withd 159 i 74 k 20 95 16 n 4 units 14 sites rlr has high coercivities unblocking temperatures and remanence intensities and appears to be a primary thermal remanence dating from 2700 ma the altered units from the gold bearing dzs carry a different remanence rlg withd 180 i 57 k 23 95 3 n 3 units 6 sites rlg also has relatively high coercivities and unblocking temperatures but its magnetization intensities are 1 2 orders of magnitude lower than those of rlr opaque minerals and silicates observed in thin section are highly altered rlg is therefore believed to be a chemical or thermochemical remanence acquired 2580 ma ago during the late stages of cooling and gold mineralization seeing as rlg characterizes the shear zone rocks but is absent from unaltered rocks outside the dzs it could be used as a rapid prospecting tool in delineating areas of alteration and possible mineralization the paleopoles for rlr 2700 ma and rlg 2580 ma link with those of the shelley lake granite 2580 ma 40ar 39ar hornblende and biotite and the matachewan hearst dikes 2450 ma u pb zircon and baddeleyite the sense of motion on the late archean early proterozoic apparent polar wander path for laurentia as defined by this sequence of paleopoles is opposite to that previously accepted

focused synthetic aperture radar processing of ice sounder data collected over the greenland ice sheet the authors developed a synthetic aperture radar sar processing algorithm for airborne spaceborne ice sounding radar systems and applied it to data collected in greenland by using focused sar phase corrected coherent averaging they improved along track resolution by a factor of four and provided a 6 db processing gain over unfocused sar coherent averaging without phase correction based on a point target analysis for a greenland ice sounding data set also they demonstrated that the focused sar processing reduced clutter and enabled them to identify bedrock interface returns buried in clutter using focused sar technique they processed data collected over a key 360 km long portion of the 2000 m contour line of southwest greenland to the best of their knowledge these are the first high quality radar ice thickness measurements over this key location moreover these ice thickness measurements have been used for improving mass balance estimates of the greenland ice sheet

how do gravel bed rivers braid sedimentary processes and bed forms leading to the onset of braiding were observed in small scale hydraulic models of gravel bed streams the laboratory streams had a variety of combinations of constant discharge and slope but identical bed material particle size distributions from initially straight channels braiding occurred by four different processes deposition and accumulation of a central bar chute cutoff of point bars conversion of single transverse unit bars to mid channel braid bars and dissection of multiple bars in these experiments the chute cutoff mechanism was the most common but the predominant braiding mechanism depends upon sediment mobility excess bed shear stress and the bed form regime at very low excess bed shear stress the central bar process dominates but at higher excess bed shear stress slip face unit bars are more common bed scour at confluences is more pronounced and propogation of alternate convergence scour and divergence deposition is more likely thus chu

analysis of bottom morphology of the david glacier drygalski ice tongue east antarctica data from radio sounding measurements have been analysed to determine the ice thickness and the bottom morphology of drygalski ice tongue antarctica the morphology and the structure of the bottom surface has been studied through an electromagnetic interpretation a function that includes the gain loss due to the geometrical shape of the reflecting surfaces has been calculated such a function has been evaluated assuming some physical electromagnetic quantities the temperature of the glacier the complex dielectric permittivity of ice sea ice and sea water the ice water interface shows both concave and convex faces toward the sounding system producing a focusing or deocusing effect detected as absolute or relative amplitude variation in the echo signal it is shown that the calculated function follows quite well the observed bottom rippled surface of the glacier tongue estimated from the time arrival measurements of the echo signal

origin of the permian triassic iberian basin central eastern spain abstract the iberian basin was an intracratonic rift basin in central eastern spain developed since early permian times the basin boundary faults were normal listric faults controlling an asymmetric extension propagating northeast with time hercynian or older lineaments controlled the orientation of the iberian basin and extension was accommodated basically in the hanging wall block by the formation of secondary grabens and a central high the basin was related with the coeval ebro catalan and cuenca mancha basins and their connections are discussed subsidence curves show that the early permian early jurassic period of extension can be subdivided into three rifting episodes and a flexural one extension factor increases from 1 17 in the northwest to 1 29 near the mediterranean coast the increasing extension rate was accommodated by transfer faults trending nne ssw more important in the levante area the rift evolution is intermittent and seems to reflect distinct stress fields the collapse of the late hercynian orogen and related increased heat flux extension and rifting is the most probable origin of the iberian basin and related basins the origin of the catalan and the valencia prebetic basins is related to the southwards migration of the hesse burgundy rift along the eastern margin of the iberian microplate

the upper permian boniches conglomerates formation evolution from alluvial fan to fluvial system environments and accompanying tectonic and climatic controls in the southeast iberian ranges central spain the boniches conglomerates fm upper permian represents the first episode of sedimentation in the southeast border margin of the iberian basin central spain the iberian basin commenced development as a rift basin running mainly nw se during the early permian and underwent its first general extensional period during the late permian the boniches fm was deposited as a small segment less than 100 km long and 9 10 km wide of the iberian basin that extended in a northeast direction during this period detailed mapping and palaeocurrent analysis have shown that the boniches fm is of a curvilinear wedge shaped morphology sediments close to the southwest main faulted border are of a maximum thickness of 230 m clear lateral variation in thickness controlled by the activity of secondary transfer faults perpendicular to the main nw se axis may be observed this network of faults permitted the formation of blocks limited laterally by the transfer faults these blocks experienced subsidence and rotation against the elevated southwest footwall block which resulted in the isolation of reduced sub basins with different sedimentary characteristics based on facies and facies association the boniches fm is thought to have evolved vertically from two main alluvial fan systems in the lowest part of the formation into fluvial braided systems flowing southeast as expected no flow orientations towards the footwall block are observed during the first episodes of the refill this may be explained by erosion or simply a lack of sedimentation due to the gentle slope the change from alluvial fan to fluvial environments is interpreted as a relatively sudden tectonic reorganization of the whole segment favouring new longitudinal fluvial drainage from a transfer zone located to the northwest three different reorganization episodes clearly marked in the boniches fm as main boundary surfaces mbs separate four members subdivided into 4 5 levels 34 m thick each level consists of fining upward successions less than 1 m thick tectonics and climatic factors clearly controlled sedimentation tectonic activity was probably of greatest importance and was conditioned by the movement of the main nw se and ne sw transfer faults the role of climate in ancient conglomerate sediments has not been well established palaeogeographical mineralogical sedimentological and clast analyses suggest that the boniches fm was deposited under humid conditions by running water the differentiation between proper alluvial fans and fluvial environments during the transition period of the boniches fro is not clear since in many recent alluvial fans braided fluvial systems are associated with fans

tectonic and climatic control of triassic sedimentation in the beryl basin northern north sea the beryl basin embayment occupies a central position along the viking graben of the northern north sea and has been a hydrocarbon play since the early 1970s detailed analysis reveals a complex half graben that was established during a rift phase of development that occurred in the early triassic teist formation after which a long period of thermal subsidence lomvi and lunde formations provided accommodation for in excess of 1000 m of sediment the teist formation sediments are complex they include shales sands and conglomerates and their superimposition on zechstein salts is indicative of both uplift and the development of a moderate relief they give way to the comparatively clean and occasionally pebbly sands of the lomvi formation for which an analysis of both bedding and texture suggests deposition by a westerly directed river system draining the hanging wall ramp the lunde formation records the spreading influence of a bajada playa complex and its eventual conversion to a more persistent lake the growing importance and eventual dominance of the succession by lacustrine sediments gives clear indication of a change in climate and this has been attributed to the rapid northward drift of pangea during the triassic period

paleohydraulic reconstruction of flash flood peaks from boulder deposits in the colorado front range nine watersheds in the colorado front range with steep bedrock channels were used to test the accuracy of paleohydraulic reconstruction of large flash floods using boulder deposits the nine basins consist of eight small ungauged basins ranging in size from 1 6 to 29 km2 and the big thompson river at the mouth of the big thompson canyon draining 790 km2 between 1923 and 1976 all nine basins had had one catastrophic flash flood the magnitude of which has been estimated by the conventional slope area method in each basin coarse boulder deposits of the large flash floods were identified and three axes of the five largest boulders were measured along with at least two profiles of the valley cross section a simple arithmetic average of two theoretical and two empirical relationships was used to estimate average flood velocity using boulder size and shape average depth was estimated as the arithmetic average of four values computed from the manning equation a regression equation for boulder size and unit stream power a relative smoothness equation and a modified shields relationship the appropriate flood width for the estimated average depth was found by iteration using the valley cross sections the paleohydraulic discharges thus computed generally underestimate conventional slope area discharge estimates on small streams by as much as 75 although the average amount is only 28 too low and the reconstructed discharge in one stream was 31 too large the big thompson river flood of 1976 was overestimated by 76 reasons for discrepancy in reconstructed peaks could include 1 the possibility that floods may have been able to move boulders larger than those available to be moved 2 overestimation of the slope area discharge because high water marks were set prior to erosion of the channel 3 underestimation of original roughness coefficients and 4 macroturbulent effects during fast deep flows the paleohydraulic technique is applied to two other streams in colorado with sedimentological evidence of large flash floods but no conventional indirect discharge estimates a small tributary to the big thompson river draining 1 8 km2 has a paleohydraulic reconstructed flood peak of about 60 m3 s from a flood in 1976 using boulders excavated from a foundation site in holocene alluvium along boulder creek in boulder colorado a paleohydraulic reconstructed flood peak of between 860 and 1 512 m3 s is calculated this is 1 4 to 2 4 times the magnitude of the estimated 500 yr flood

aeromagnetic interpretation of the kirkland lake larder lake portion of the abitibi greenstone belt ontario high resolution aeromagnetic data from the larder lake kirkland lake region have been analyzed to develop optimum maps for geologic interpretation the use of the apparent susceptibility technique has led to a map that shows clearly the major lithologies in a major synclinorium in the abitibi greenstone belt calc alkaline volcanics of the blake river group are weakly magnetic but show ring like anomalies associated with intrusives where magnetite has been generated in the country rock alternating bands of mg rich and fe rich tholeiites of the kinojevis group show a strong magnetization associated with the fe rich phases gabbroic intrusions underlain by serpentine and peridotite give strong levels of magnetization these various units have been sampled and it is shown that the susceptibility is not high enough to account for the anomalies rather the anomalies are associated with the mean natural remanent magnetization in the formations sampled these studies have led to a revised geological map of this region

geology and fluid characteristics of the ulu sokor gold deposit kelantan malaysia implications for ore genesis and classification of the deposit abstract the ulu sokor gold deposit is one of the most famous and largest gold deposits in malaysia and is located in the central gold belt this deposit consists of three major orebodies that are related to ns and ne striking fractures within fault zones in permian triassic meta sedimentary and volcanic rocks of the east malaya block the faulting events represent different episodes that are related to each orebody and are correlated well with the mineralogy and paragenesis the gold mineralization consists of quartz dominant vein systems with sulfides and carbonates the hydrothermal alteration and mineralization occurred during three stages that were characterized by i silicification and brecciation ii carbonatization sericitization and chloritization and iii quartz carbonate veins fluid inclusions in the hydrothermal quartz and calcite of the three stages were studied the primary co 2 ch 4 h 2 o nacl fluid inclusions in stage i are mostly related to gold mineralization and display homogenization temperatures of 269 389 c salinities of 2 77 11 89 wt nacl equivalent variable co 2 contents typically 5 29 mol and up to 15 mol ch 4 in stage ii gold was deposited at 235 398 c from a co 2 ch 4 h 2 o nacl fluid with a salinity of 0 83 9 28 wt nacl equivalent variable co 2 contents typically 5 63 mol and up to 4 mol ch 4 the 18 o h 2 o and d values of the ore forming fluids from the stage ii quartz veins are 4 5 to 4 8 and 44 to 42 respectively and indicate a metamorphic hydrothermal origin oxygen fugacities calculated for the entire range of t p x co 2 conditions yielded log f o 2 values between 28 95 and 36 73 for stage i and between 28 32 and 39 18 for stage ii these values indicate reduced conditions for these fluids which are consistent with the mineral paragenesis fluid inclusion compositions and isotope values the presence of daughter mineral bearing aqueous inclusions is interpreted to be a magmatic signature of stage iiia combined with the oxygen and hydrogen isotopic compositions 18 o h 2 o 6 8 to 11 9 d 77 to 62 these inclusions indicate that the initial fluid was likely derived from a magmatic source in stage iiib the gold was deposited at 263 to 347 c from a co 2 ch 4 h 2 o nacl fluid with a salinity of 5 33 to 11 05 wt nacl equivalent variable co 2 contents typically 9 15 mol and little ch 4 the oxygen and hydrogen isotopic compositions of this fluid 18 o h 2 o 8 1 to 8 8 d 44 to 32 indicate that it was mainly derived from a metamorphic hydrothermal source the co 2 h 2 o ch 4 nacl fluids that were responsible for gold deposition in the stage iiic veins had a wide range of temperatures 214 483 c salinities of 1 02 to 21 34 wt nacl equivalent variable co 2 contents typically 4 53 mol and up to 7 mol ch 4 the oxygen and hydrogen isotopic compositions 18 o h 2 o 8 5 to 9 8 d 70 to 58 were probably acquired at the site of deposition by mixing of the metamorphic hydrothermal fluid with deep seated magmatic water and then evolved by degassing at the site of deposition during mineralization the log f o 2 values from 28 26 to 35 51 also indicate reduced conditions for this fluid in stage iiic moreover this fluid had a near neutral ph and 34 s values of h 2 s of 2 32 to 0 83 which may reflect the derivation of sulfur from the subducted oceanic lithospheric materials the three orebodies represent different gold transportation and precipitation models and the conditions of ore formation are related to distinct events of hydrothermal alteration and gold mineralization the gold mineralization of the ulu sokor deposit occurred in response to complex and concurrent processes involving fluid immiscibility fluid rock reactions and fluid mixing however fluid immiscibility was the most important mechanism for gold deposition and occurred in these orebodies which have corresponding fluid properties structural controls geologic characteristics tectonic settings and origins of the ore forming matter these characteristics of the ulu sokor deposit are consistent with its classification as an orogenic gold deposit while some of the veins are genetically related to intrusions

two phase syntectonic gold mineralization and barite remobilization within the main ore body of the golden giant mine hemlo ontario canada abstract structural analysis of the central part of the hemlo gold deposit in the hemlo heron bay greenstone belt has revealed four generations of deformation structures d1 d4 the second d2 and fourth d4 deformations significantly influenced the orebody and controlled the localization of gold mineralization development of d3 dextral shearing during retrogressive conditions resulted in strain partitioning around the feldspathic orebody such that this deposit appears to be controlled by the hemlo shear zone however the orebody dominantly preserves vertical d2 parasitic folds rather than d3 structures the earliest occurrence of gold is with molybdenite as s1 inclusion trails in vanadium muscovite grains that grew during d2 this suggests that the gold deposit was emplaced by at least early d2 syngenetic banded barite was partially dissolved transported and redeposited during each deformation event and in particular in association with brittle deformation that occurred during d4 microstructural relationships indicate two distinct generations of gold the first generation is associated with molybdenite and potassic alteration and was deposited before or early in d2 during progressive amphibolite facies metamorphism the second generation formed by redistribution and concentration of gold together with stibnite in ductile brittle d4 structures after peak metamorphic conditions

the evolution of aqueous vapor from silicate melts effect on oxygen fugacity abstract the simplest possible aqueous vapor evolved from an iron bearing magma under normal conditions is an h 2 o h 2 mixture hydrogen is produced by the oxidation of fe ii to fe iii by water in the magma yielding an increase in f o 2 equations are derived which model this mass transfer process the resulting differential equation expresses the change in magmatic f o 2 as a function of a change in n 1 h 2 o the vapor evolution progress variable the calculations demonstrate that in this simple scheme very iron poor magmas h 2 o feo are required to produce significant increases in magmatic f o 2 the incremental increase in o 2 during vapor evolution becomes progressively smaller as o 2 increases with this process becoming highly inefficient as the hematite stability field is approached other more complete processes involving meteoric water assimilation of altered rocks and subsolidus processes may produce the observed increase in f o 2 inferred to have occurred in systems of normal iron contents in low iron systems such as the high silica rhyolitic magmas associated with climax type porphyry molybdenum systems high oxygen fugacities may be obtained by this mechanism

granite hosted gold mineralization in the midlands greenstone belt a new type of low grade gold deposit in zimbabwe in 1992 the ford gold deposit was rediscovered during field work in the kwekwe district near the indarama mine approximately 200 km southwest of harare zimbabwe based on diamond drilling and open pit operations estimated ore reserves are at least 3 mt with an average gold content of 2 5 g t the gold deposit is located within a porphyritic granite dike with a thickness of 20 50 m striking 800 m nnw sse it dips 60 70 to the ne and intrudes a volcano sedimentary sequence of tholeiitic basalts acid volcanics and banded iron formations of the bulawayan group 2900 2700 ma the intrusion of the dike occurred at 2541 17 ma pb pb step leaching technique within a second order structure and is related to displacement along transcrustal deformation zones such as the sherwood and taba mali deformation zones gold mineralization is confined to the s shaped part of the dike intrusion at the present stage of mining the deposit is characterized by the absence of major veins the occurrence of disseminated pyrite throughout the orebody and a distinct alteration pattern comparable to that of porphyry copper deposits the central zone of the dike shows a typical k feldspar albite sericite pyrite biotite alteration followed by a narrow external propylitic zone native gold with an average ag content of 5 wt and a grain size of 5 100 m is rare and occurs within pyrite and secondary k feldspar sulphide mineral separates of pyrite and minor arsenopyrite probably contain invisible gold up to 120 ppm amenable to cyanidation anomalously high gold values of 7 ppm have been found in the transition between the k feldspar albite sericite pyrite alteration and the propylitic zone indicating that the mineralizing fluids have experienced major physico chemical changes in the transition zone the regional tectonic position of the orebody suggests that the emplacement of the granite and the gold mineralization are structurally controlled the pb isotope composition of several leachates of pyrite indicate isotope disequilibrium with magmatic minerals and point to a contamination of the mineralizing fluid by pb from older sedimentary sources stable isotope geochemistry of sulphides and carbonates as well as the metallogeny of the deposit compare to shear zone hosted gold mineralization in the kwekwe district for which a deep crustal origin has been discussed although this study documents contrasting evidence for a porphyry gold versus a shear zone type of mineralization it is suggested that gold bearing fluids were syntectonically introduced into a ductile shear zone within the granite dike either during cooling of the intrusion or later in archaean or early proterozoic times

source and timing of gold and other mineralization in the red lake area northwestern ontario based on lead isotope investigations the problems of the timing and source of gold mineralization and the sulfidation mechanism in the red lake area north western ontario have been addressed using more than 300 pb isotope analyses o

determination of the ice dielectric permittivity using the data of the test in antarctica of the ground penetrating radar for mars 98 mission a ground penetrating radar will be integrated inside the guiderope ballast of the mars 98 balloon mission a prototype of this impulse system working in the 5 15 mhz band was tested close to dumont d urville the french antarctic station in february 1993 the authors obtained a large set of profiles in cold ice with a glacier thickness from 200 to about 900 m for each depth the measured echoes are very clear with a good signal to noise ratio snr in this paper the authors firstly describe the performances of the radar and they study the electromagnetic propagation in the antarctica glacier this knowledge allows them to use the frequency wavenumber migration to focus the signal to increase the snr and to rebuild an image of the subsurface the migration process gives a good estimation of the real part of the permittivity i e the velocity the fact that the signal comes from different depths is used to measure the imaginary part of the permittivity which defines the ice attenuation the spectral analysis gives its frequency dependence

phase field imaging the electromagnetic equivalent of seismic migration an alternative approach to the interpretation of electromagnetic em data is to downward continue the observations to construct a two dimensional resistivity image of the medium that produced them the downward continuation can be done in a straightforward manner by drawing a parallel between the em and acoustic wave equations with appropriate approximations and identification of specific terms that are equivalent and with transformation from an initial value problem to a boundary value problem em data can be imaged using any of the methods originally developed for migration of seismic data the method we chose here is claerbout s one way finite difference wave equation migration the algorithm is implemented in the frequency domain independent images of relative reflectivity are obtained by processing e and h pseudosections separately the best estimate of the actual reflector position is the region of coincidence of the two images the same approach can be used in reverse for modeling the em respo

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

geochemical evidence for magmatic fluids in porphyry copper mineralization the koloula igneous complex comprises 26 different intrusive phases that have been divided into two major magmatic episodes cycle 1 intrusions 4 5 ma and cycle 2 intrusions 2 4 to 1 5 ma the cycle 2 intrusions are further divided into the inamumu zoned pluton izp which is composed of 6 concentrically disposed quartz diorite and tonalite units and several satellite intrusions the izp is host to porphyry copper mineralization whereas the cycle 1 and cycle 2 satellite intrusions are barren presently exposed mineralization in the izp a system represents the deeply eroded core of a porphyry copper system where widely spaced veinlet alteration envelopes 1 mm thick are separated by large volumes of unaltered rock

bedload sheets in heterogeneous sediment field observations in streams with beds of coarse sand and fine gravel have revealed that bedload moves primarily as thin migrating accumulations of sediment and coarse grains cluster at their leading edge these accumulations are one or two coarse grains high and are much longer 0 2 0 6 m long in sand 0 5 2 0 m in fine gravel than their height the authors propose the term bedload sheet for these features and the authors argue that they result from an instability inherent to bedload movement of moderately and poorly sorted sediment in essence coarse particles in the bedload slow or stop each other trap finer particles in their interstices and thus cause the coarse particles to become mobile again bedload sheets develop on the stoss side of dunes causing the dune to advance incrementally with the arrival of each sheet successive deposition of coarse sediment from the leading edge followed by fine sediment may generate the grain size sorting that distinguishes cross bedding available flume experiments and field observations indicate that bedload sheets are a common but generally unrecognized feature of heterogeneous sediment transport

the porphyry gold association in the norseman wiluna belt of western australia implications for models of archaean gold metallogeny abstract porphyritic minor intrusions felsic intermediate porphyries and lamprophyres occur in the vicinity of many gold deposits in the archaean norseman wiluna belt of western australia but are not restricted to this environment unlike the abitibi belt of canada there is no correlation between the presence of such intrusions and the economic status of a deposit the timing of intrusive activity with respect to spatially associated mineralization is variable with mainly instances of pre sometimes 10 ma earlier and some examples of post ore emplacement being recorded in many cases the porphyry gold association reflects the importance of structural control to the localization of mineralization intrusions may exploit the same zones of crustal weakness as the ore fluids although such a relationship need not imply contemporaneity or may act as structural traps for mineralization owing to rheological contrast between intrusion and country rock the composition and petrogenesis of the minor intrusions are both variable and there is no evidence of a specific suite of intrusions preferentially associated with mineralization spatial temporal and petrogenetic considerations preclude direct evolution of the gold bearing fluids from the minor intrusions and militate against magmatic theories of ore genesis rather both the igneous activity and the mineralization are viewed as expressions of a deep seated tectono thermal event that affected the yilgarn block in the late archaean

mineralogical fluid inclusion and stable isotope constraints on mechanisms of ore deposition at the samgwang mine republic of korea a mesothermal vein hosted gold silver deposit the samgwang mine is located in the cheongyang gold district cheonan metallogenic province of the republic of korea it consists of eight massive gold bearing quartz veins that filled ne and nw striking fractures along fault zones in precambrian granitic gneiss of the gyeonggi massif their mineralogy and paragenesis allow two separate vein forming episodes to be recognized temporally separated by a major faulting event the ore minerals occur in quartz and calcite of stage i associated with fracturing and healing of veins hydrothermal wall rock alteration minerals of stage i include fe rich chlorite fe fe mg ratios 0 74 0 81 muscovite illite k feldspar and minor arsenopyrite pyrite and carbonates sulfide minerals deposited along with electrum during this stage include arsenopyrite pyrite pyrrhotite sphalerite marcasite chalcopyrite galena argentite pyrargyrite and argentian tetrahedrite only calcite was deposited during stage ii fluid inclusions in quartz contain three main types of c o h fluids co2 rich co2 h2o and aqueous inclusions quartz veins related to early sulfides in stage i were deposited from h2o nacl co2 fluids 1 500 5 000 bar average 3 200 with thtotal values of 200 c to 383 c and salinities less than about 7 wt nacl equiv late sulfide deposition was related to h2o nacl fluids 140 1 300 bar average 700 with thtotal values of 110 c to 385 c and salinities less than about 11 wt nacl equiv these fluids either evolved through immiscibility of h2o nacl co2 fluids as a result of a decrease in fluid pressure or through mixing with deeply circulated meteoric waters as a result of uplift or unloading during mineralization or both measured and calculated sulfur isotope compositions 34sh2s 1 5 to 4 8 of hydrothermal fluids from the stage i quartz veins indicate that ore sulfur was derived mainly from a magmatic source the calculated and measured oxygen and hydrogen isotope compositions 18oh2o 5 9 to 10 9 d 102 to 87 of the ore forming fluids indicate that the fluids were derived from magmatic sources and evolved by mixing with local meteoric water by limited water rock exchange and by partly degassing in uplift zones during mineralization while most features of the samgwang mine are consistent with classification as an orogenic gold deposit isotopic and fluid chemistry indicate that the veins were genetically related to intrusions emplaced during the jurassic to cretaceous daebo orogeny

the hemlo gold deposit ontario an example of melting and mobilization of a precious metal sulfosalt assemblage during amphibolite facies metamorphism and deformation the timing of mineralization at the hemlo gold deposit has long been a controversial issue we present arguments that use partial melting of the ore assemblage to explain the mechanism of ore mobilization and resolve problems with the model of premetamorphic mineralization the results have implications for mine exploitation and exploration strategies we show that the ore mineral assemblage underwent partial melting during middle amphibolite facies metamorphism 600 650 c 6 7 kbars primarily through breakdown of stibnite and arsenopyrite in a high s2 environment concurrent deformation led to segregation of the resulting sb and as rich sulfosalt melt interaction between this melt and a range of unmelted sulfides led to further melting and incorporation of other elements into the melt the gold bearing melt was mobilized from compressional high strain sites into dilational domains such as boudin necks and extensional fractures developed in competent lithologies ore minerals that did not melt significantly pyrite molybdenite pyrrhotite and sphalerite were not extensively mobilized and largely remained within high strain compressional domains this segregation of melt from residue thus resulted in the observed heterogeneous distribution of ore minerals within the deposit crystallization of the sulfosalt melt produced a diverse suite of ore minerals dominated by stibnite and realgar and containing an array of rare sulfosalts native elements intermetallic compounds and tellurides some sulfosalt melt persisted to low temperature 300 c allowing continued small scale localized mobilization during late deformation although gold occurs at moderate concentrations within the compressional high strain domains it is particularly concentrated in the dilational domains a consequence of its mobilization within a sulfosalt melt our model of partial melting of the ore mineral assemblage with consequent mobilization explains how ore minerals that are unstable even at greenschist facies conditions came to be hosted in structures that formed at or near the peak of amphibolite facies metamorphism

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

setting characteristics and age of the andean porphyry copper belt in colombia three distinct porphyry copper subbelts are defined in the colombian andes 1 a western subbelt emplaced during the early to middle eocene in an oceanic domain underlain by ophiolitic basement along the western side of the western cordillera 2 a composite eastern subbelt generated during the middle jurassic to earliest cretaceous in a continental domain underlain by elements of the guyana shield along the eastern side of the central cordillera and the western side of the eastern cordillera and between the two 3 a central subbelt formed in the early to late miocene at the contact of the oceanic and continental domains along the cauca patia depression and its flanks k ar geochronometry undertaken as part of this study provided preferred minimum ages of 54 7 or 1 3 m y for murindo 48 1 or 1 0 m y for acandi and 42 7 or 0 9 m y for pantanos pegadorcito in the western subbelt 166 or 4 m y for mocoa 166 or 4 m y for dolores 144 or 3 m y for california and 131 or 2 m y for infierno chili in the eastern subbelt and 17 4 or 0 4 m y for piedrasentada in the central subbelt the porphyry copper prospects are associated with dacite to tonalire porphyry stocks which in the western and eastern subbelts intruded batholiths emplaced perhaps 15 to 30 m y earlier but which in the central subbelt are isolated within metamorphic or sedimentary host rocks the porphyry copper systems exhibit a variety of alteration patterns with potassium silicate and sericitic alteration important in the highest grade prospects and propylitization predominant in low grade occurrences none of the prospects displays significant supergene enrichment although porphyry coppers in the continental domain tend to be more molybdenum rich than those in the oceanic domain gold rich prospects occur in both settings as do major lode gold deposits the jurassic and miocene subbelts are interpreted to have been emplaced during eastward subduction at andean type continental margins whereas the western eocene subbelt could have been generated in either a modified andean type setting or in an intraoceanic island arc prior to its accretion to the continental edge

magnetite chemistry as a provenance indicator in archean metamorphosed sedimentary rocks abstract conventional provenance studies of high grade e g amphibolite facies metamorphic sandstone are limited due to intense recrystallization destruction of original minerals and growth of new minerals magnetite is a heavy mineral common in a wide range of sedimentary rocks it can originate from a wide range of rock sources from high temperature to low temperature magmatic metamorphic or hydrothermal environments laser ablation la icp ms and electron microprobe analytical techniques allowed determination of a wide range of trace elements at sub ppm levels in magnetite to identify the provenance of two archean sedimentary formations in eeyou istchee baie james quebec canada results were plotted on multi element diagrams the most compatible elements in magnetite were identified as the most discriminant elements to differentiate four potential different rock sources for the magin formation overlap between the spectra of the magin and keyano formations substantiate the existence of a common source interbedded conglomerate magnetite bearing clasts were examined to determine potential source rocks mafic clasts apparently do not contain magnetite detrital magnetites analyzed have low ti values that would support either felsic to intermediate plutonic or a hydrothermal source the trace element spectra of detrital magnetite from the sandstone beds were compared to magnetite spectra from conglomerate clasts of banded iron formation and felsic to intermediate plutonic rocks only magnetites from felsic plutonic rocks have a signature similar to those from the sandstone to further substantiate a felsic plutonic source a detailed study of magnetite chemistry from ten felsic and intermediate regional plutons from a regional databank allowed us to recognize that each of these plutons has a particular signature on the basis of wide variations in ni and cr from this data base four individual plutons were identified as potential sources for the magin formation recently published magnetite discrimination diagrams proposed for mineral deposits can be applied to sedimentary magnetite provenance however our database shows the importance of identifying low ti magnetite from felsic rocks since these could be misidentified as low ti magnetite from hydrothermal mineral deposits thus we propose improvement to these diagrams by differentiating magnetite from felsic magmatic low ni cr and hydrothermal high ni cr sources before applying the mineral deposit discrimination diagrams