origin of the intrusion related lang vai gold antimony district northeastern vietnam constraints from fluid inclusions study and c o s pb isotope systematics abstract the lang vai ore district located in the central part of the lo gam domain in the northeast vietnam contains at least three deposits khoun puc lang vai and lung luong the general paragenetic sequences for these deposits may be represented by the following mineral associations from early to late i arsenopyrite pyrite native gold sphalerite ii bi rich pb sb sulfosalts iii bi poor pb sb sulfosalts iv sb sulfosalts v sb rich minerals native antimony and vi pb rich sb sulfosalts as a distal mineral association three major types were recognized within the primary fluid inclusions based on the phases present at room temperature including v type vapor rich inclusions l type liquid rich inclusions and c type co2 rich inclusions the early au as stage quartz crystals contain the v and l type fluid inclusions the results indicate that the initial ore forming fluid belonged to a co2 ch4 h2o nacl system characterized by high temperatures 290 352 c and variable to moderate salinities 3 16 13 89 wt nacl which are analogous to reduced intrusion related ore forming fluids that exhibit high homogenization temperatures and moderate salinities the quartz crystals from the bi pb sb mineral paragenesis occurred only at the khoun puc deposit contain both v and l type fluid inclusions and characterized by high temperatures mainly 304 340 c and moderate salinities 6 28 8 22 wt nacl equiv the quartz crystals from the middle hydrothermal stage contain the v and l type fluid inclusions that yield moderate homogenization temperatures 240 290 c and variable salinities 3 3 8 2 wt nacl equiv these features indicate that the fluid evolved into an co2 ch4 h2o nacl system at moderate temperatures lower ch4 concentrations and variable salinities thus indicating changing physicochemical conditions in the last sb stage the lang vai deposit and pb sb stage the lung luong deposit the ore forming fluid belongs to co2 h2o nacl system which is characterized by low temperature 180 240 c enrichment of co2 and medium low salinity 1 12 9 5 wt nacl equiv that corresponded to typical fluids which formed the sb and distal ag pb zn veins of the irgs deposits in the tintina gold province of alaska usa and yukon canada the fluid inclusion studies and laser raman spectroscopy suggest that the early fluids were dominated by ch4 whereas the late fluids by co2 our study suggests that the fluid boiling and accompanying decrease in the solubility of gold bisulfide complex played an important role in gold deposition at the khoun puc and lang vai deposits the trapping pressures estimated from the boiling fluid inclusions were 123 343 mpa during the ore forming process this suggests an alternating lithostatic hydrostatic fluid system controlled by a fault valve activity at a depth of 12 9 15 2 km the characteristics of the s isotopes and fluid inclusions suggest that the ore forming fluids were of magmatic origin during mineralization process the fluid rock interaction between the fluids and host rocks resulted in the increase of 34s values of the fluids as reflected in the range of sulfur isotope from the different deposits on a plumbotectonic diagram the sulfides show correlations between 206pb 204pb and both 207pb 204pb and 208pb 204pb which suggest a two component mixing between a high radiogenic end member and another low radiogenic end member the 13cpdb vs 18osmow study clear show that c and o in the khoun puc ore forming fluids were most likely to be derived from the magma with limited contribution from the carbonate host rocks predominantly magmatic origin of hydrothermal fluids wherein the calcite separates from the lang vai and lung luong deposits have 18osmow values higher than those of the khoun puc suggesting that the carbonate host rocks may have provided more c and o for ore forming fluids in these deposits the results combined with existing data on the regional geology ore geology ore geochemistry age of mineralization and tectonic setting indicate that the lang vai ore district is an intrusion related gold system

banktop responses to quaternary fluctuations in sea level recorded in periplatform sediments periplatform sediment from a 12 m core recovered from northwest providence channel bahamas contains a geochemical and paleontological record of sea surface temperatures ice volumes and the response of banktops to highstands of sea level a comparison of these data suggests that fluctuations of carbonate mineralogy in periplatform sediments result from fluctuations of sea level and from patterns of banktop sedimentation highstands of sea level that flood carbonate platforms are recorded in periplatfonn sediments as abrupt increases of exported sr rich aragonite derived from banktop orgiuiisms superposed on a background of sr poor aragonite pteropods and calcite foraminifera and coccoliths derived from planktonic sources the pulses of banktop sediment coincide with increases of water temperature determined from foraminiferal assemblages and with decreases in ratios of oxygen isotopes indicating decreased ice volume and rising sea level following these abrupt changes is a more gradual decline in bank derived sediment although paleotemperatures from foraminiferal assemblages and oxygen isotopic data clearly show that warm conditions and a highstand of sea level persist we suggest that this decrease of offbank transport is part of autocyclic sedimentation patterns of shallow water carbonate environments offbank transport is restricted as reefs sand shoals and islands reach sea level also green algal production may decline because progradation of tidal flats decreases lagoon area and the hydrologic and ecologic conditions change as lagoons are filled

model for the origin of the troodos massif cyprus and other mideast ophiolites any comprehensive model for the origin of the troodos complex and other mideast ophiolite complexes must explain the geochemical evidence for subduction zone involvement the thin inferred oceanic crust the extensional environment indicated by sheeted dikes the existence of fault zones perpendicular to the inferred spreading axes and the discontinuous nature of ophiolite exposures around the arabian block the andaman sea region of the indian ocean may provide an actualistic model for the origin of these ophiolites there spreading takes place in short segments above a subduction zone in the region of active spreading the andaman sea model substantially accounts for the known geologic and geophysical data from the circum arabian ophiolite belt and it leads to some predictions about the structural and geophysical relationships to be expected in this important belt the model also predicts that andaman sea spreading center magmas may be similar in composition to those found in the mideast ophiolites

carbonate platforms of passive extensional continental margins types characteristics and evolution abstract carbonate platforms of extensional margins may be grouped into several major categories homoclinal ramps have gentle slopes into deep water may have skeletal or ooid pellet sand shoal complexes that grade without break in slope into deep ramp nodular limestone and then into pelagic hemipelagic basin facies they generally lack significant slump and sediment gravity flow deposits in the deeper water facies distally steepened ramps differ from the above in having a marked increase in slope at the seaward edge of the deep ramp and abundant slumps slope breccias and turbidites however clasts of shallow platform margin facies are generally absent from breccias rimmed shelves have linear trends of shelf edge lime sands and reefs a marked increase in slope into deep water and foreslope and slope sands breccias with clasts of platform margin rocks and turbidites grading seaward into basin hemipelagic pelagic muds they may be divided into accretionary bypass and erosional margins isolated platforms are broad flat topped shallow platforms surrounded by deeper water few hundred meters to 4 km deep many are bypass margins but accretionary and erosional margins also occur finally incipiently to completely drowned or open platforms may develop by rapid submergence of ramps shelves or isolated platforms shallow platform margin facies are shifted landward and the earlier shallow water platform is covered with transgressive lags and deeper water blankets of hemipelagic or pelagic facies or open marine whole fossil wackestone the carbonate prisms commonly develop above a basal clastic phase ramps develop early and evolve into rimmed shelves however with drowning rimmed shelves may evolve up into ramps rimmed shelves may also develop into ramps where miogeoclinal faces prograde into filling marginal basins carbonate miogeocline deposition terminates when the shelf becomes a prograding clastic shelf or where it becomes part of a collisional orogen the various platform types may be recognized from continental margin sequences ranging from proterozoic to holocene in age

a reconstruction of moorhead and emerson phase environments along the eastern margin of glacial lake agassiz rainy river basin northwestern ontario mapping of quaternary geology in the rainy river lowland northwestern ontario resulted in discovery of several fossil bearing localities organic remains are associated with both the moorhead and

geological fluid inclusion h o s pb isotope and ar ar geochronology constraints on the genesis of the nancha gold deposit southern jilin province northeast china abstract the nancha gold deposit located in the central part of southern jilin province in the northeastern portion of the north china craton contains orebodies hosted in a proterozoic metamorphosed volcanic sedimentary sequence the distribution of the orebodies is controlled by nne trending brittle ductile shear zones and faults the gold orebodies consist of auriferous quartz veins and auriferous altered rocks mineralization can be divided into three stages 1 quartz pyrite 2 quartz gold polymetallic sulfide and 3 quartz carbonate with gold being introduced mainly in the second stage three types of fluid inclusions were identified in the vein mineral assemblages based on petrography and laser raman spectroscopy nacl h 2 o w type co 2 h 2 o c type and pure co 2 pc type crystals in the early quartz pyrite stage veins mainly contain c type primary fluid inclusions and rare pc type inclusions the fluid inclusions in these veins completely homogenize at temperatures of 273 432 c and show low salinities of 0 63 7 78 wt nacl equiv in the middle quartz gold polymetallic sulfide stage all three types of fluid inclusions were observed these fluid inclusions homogenize at temperatures of 132 to 255 c and show salinities of 0 83 11 72 wt nacl equiv in contrast crystals in the late quartz carbonate stage contain only w type fluid inclusions that show homogenization temperatures of 132 255 c and salinities of 0 35 7 86 wt nacl equiv these data indicate that the metallogenic system evolved from a co 2 rich metamorphogenic fluid to a co 2 poor fluid due to inputs of meteoric waters fluid boiling and mixing caused the rapid precipitation of sulfides and gold trapping pressures estimated from boiling c type fluid inclusions were 152 367 mpa in the ore forming stage this suggests an alternating lithostatic hydrostatic fluid system controlled by a fault valve activity at a depth of 13 8 15 2 km one hydrothermal sericite sample from an auriferous quartz vein yielded an 40 ar 39 ar isotopic plateau age of 170 1 1 9 ma indicating that mineralization occurred in the middle jurassic and was unrelated to the volcanics and intrusions in the mineralized area the characteristics of h o s pb isotopes and fluid inclusions suggest that the ore forming fluids were of metamorphic origin with the s originating from proterozoic crustal components and the pb originating from a mixture of ore forming metamorphogenic fluids and host rocks the results combined with existing data on the regional geology ore geology fluid inclusions h o s pb isotope geochemistry age of mineralization and tectonic setting indicate that the nancha gold deposit was an orogenic type system that formed in a middle jurassic accretionary orogenic regime following subduction of the paleo pacific plate beneath the eurasian continent

giant quartz vein systems in accretionary orogenic belts the evidence for a metamorphic fluid origin from δ 15 n and δ 13 c studies abstract nitrogen isotope compositions of hydrothermal micas in giant structurally hosted quartz vein systems place constraints on the origin of the hydrothermal fluids the vein systems are from neoarchean terranes in the superior province of canada and the norseman terrane western australia the four quartz vein systems studied in different terranes formed at metamorphic grades ranging from lower greenschist to lower amphibolite facies coevally with metamorphism of the host terrane nitrogen resides predominantly as nh 4 in hydrothermal mica for lower to upper greenschist facies quartz veins n contents and 15 n values of micas are between 40 and 200 ppm and 15 and 21 respectively whereas in quartz veins formed at the greenschist to amphibolite transition and lower amphibolite facies micas have n contents of 20 70 ppm and 15 n of 11 24 in contrast micas and k feldspars from granitoids in the neoarchean abitibi and red lake greenstone belts are characterized by systematically lower 15 n of 5 to 5 and generally lower n contents of 20 50 ppm comparable to other granitoids carbon and oxygen isotope compositions of hydrothermal ferroan dolomite and calcite show systematic depletions with increasing metamorphic grade the mean values range from 2 2 to 3 7 for 13 c and 13 8 to 12 3 for 18 o in veins formed at lower to upper greenschist facies but from 5 8 to 7 1 for 13 c and 11 4 to 9 8 for 18 o at higher metamorphic grades nitrogen isotope compositions rule out mantle 15 n mean 5 magmatic 15 n 5 to 15 n mean 4 4 2 0 for the quartz veins accordingly the results are consistent with fluids derived from metamorphic dehydration of oceanic crust and sediments within accretionary orogenic belts

geology fluid inclusion and stable isotopes o s of the hetaoping distal skarn zn pb deposit northern baoshan block sw china abstract the hetaoping zinc lead deposit is located in the northern baoshan block sanjiang region sw china the ore deposit comprises massive orebodies in the lower part and lenticular and vein like orebodies in the upper part both of which are hosted in the marbleized upper cambrian limestone and slate of the hetaoping formation three mineralization stages of hetaoping skarn system have been recognized based on petrographic observation which are pre ore stage pyroxene garnet actinolite epidote magnetite syn ore stage sulfides quartz calcite fluorite and post ore stage calcite quartz chlorite andradite and hedenbergite are dominant in pre ore garnet and pyroxene respectively ore minerals consist of mainly pyrite sphalerite chalcopyrite bornite and galena three types of fluid inclusions have been identified in hetaoping including primary two phase a type primary three phase b type and secondary two phase c type inclusions based on fluid inclusion microthermometric study the fluids forming the hetaoping skarn minerals and sulfides evolved from high moderate temperature 255 498 c and low moderate salinity 5 0 18 0 wt nacl equiv in pre ore stage through moderate low temperature 152 325 c and low salinity 0 4 14 2 wt nacl equiv in syn ore stage to low temperature 109 205 c and low salinity 0 9 10 0 wt nacl equiv in post ore stage the sulfide 34 s values range from 3 7 to 7 1 mean 5 2 n 29 indicative of a dominantly magmatic sulfur origin silicate and carbonate oxygen isotopes give calculated 18 o h2o ranges of 3 9 11 1 in prograde stage 0 9 to 4 6 in early retrograde stage and 1 3 to 2 9 in late retrograde stage syn ore stage the oxygen isotope data reveal that the prograde fluid in hetaoping could be primarily magmatic which has been mixed significantly with meteoric water in the late retrograde stage such a fluid mixing process is considered to be a key factor controlling ore precipitation

local to regional scale structural controls on mineralisation and the importance of a major lineament in the eastern mount isa inlier australia review and analysis with autocorrelation and weights of evidence although major crustal lineaments may play an important role in mineralisation the relationship between lineaments and mineral deposits can be quite cryptic and structural controls may vary as a function of scale along lineaments major lineaments alone may be of limited use for detailed target generation the cloncurry lineament in the eastern part of the mount isa inlier is a crustal scale structure defined by potential field derived worms weights of evidence quantifies the association between mineral occurrences and this lineament autocorrelation is used to recognise structural controls on mineralisation at different scales by progressively limiting the lengths of the vectors between mineral occurrence points in the autocorrelation plot the weights of evidence analysis shows that au au cu cu au and cu deposits have a positive spatial correlation to the cloncurry lineament which suggests it that acted as a primary crustal scale control on the localisation of cu and au through focussing mineralisation systems on a broad scale however autocorrelation defines a variety of local structural controls which can be interpreted as shear zones variably oriented fault sets en echelon fault arrays and potentially the orientation of bedding and or iron formations which localise fluid flow and mineral deposition at finer scales the results suggest that major lineaments defined by geophysical contrasts can be used in conjunction with techniques of spatial analysis for targeting structurally controlled mineralisation in areas under thin cover adjacent to mineralised terrains such as the mt isa inlier

longitudinal transport of turbidity currents a model study of horgen events experiments were carried out in a 10 6 m basin to simulate turbidity currents generated by the horgen slumping events of 1875 the conditions for kinematic similarity were satisfied and the experiments gave further insight into the mechanics of transport triggered by the horgen slumps the experimental turbidity currents laid down thick deposits on a subaqueous fan and thin sheets of turbidite on the floor of the elongate basin through longitudinal transport comparable with the simulated deposits in lake zurich it is concluded that longitudinal transport is a general phenomenon of turbidity currents

ore controls in the charters towers goldfield ne australia constraints from geological geophysical and numerical analyses the approach taken in this paper namely synthesising a wealth of previous information with new data and a genetic model in combination with integrated numerical analyses led to new insights into the geological controls on the localisation of auriferous veins and residual prospectivity of the charters towers goldfield ne australia the method also has implications for the assessment of other mature goldfields worldwide despite a number of different ore controls having operated within the charters towers goldfield the controlling factors can be linked to a single genetic model for orogenic granitoid hosted lode gold mineralisation in a brittle deformation regime d4 of ne sw to nne ssw shortening under conditions of supralithostatic fluid pressure and low stress difference spatial autocorrelation results suggest district scale alignment of the auriferous veins parallel to and overlapping with the ese wnw to e w striking charters towers ravenswood lineament a major crustal boundary in the basement to the ravenswood batholith at the camp scale auriferous veins have abundance and proximity relationships with nw se nnw sse ne sw and ene wsw oriented lineaments suggesting that structures that controlled gold deposition in one camp did not necessarily control mineralisation in other camps fractal dimensions obtained with the box counting method range from 1 02 to 1 10 whereas veins in the charters towers city camp are characterised by a significantly higher fractal dimension of 1 28 this discrepancy may be taken to imply that most or all outcropping and near surface deposits within the charters towers city camp have been found and that new discoveries are more likely to occur at greater levels of depth or outside the boundaries of this camp the new understanding has implications for the assessment of the residual prospectivity of the charters towers goldfield where large areas of prospective rock types and structures e g approximately 40 of the charters towers ravenswood lineament are hidden under cover this parameter space was inaccessible to the historic prospectors and has received relatively little attention from recent explorers the following steps are suggested for the development of a targeting strategy for lode gold exploration in areas of the goldfield under cover 1 identify from geological and geophysical data the ene wsw 15 and nnw sse 15 striking structures and geological boundaries within a 20 km wide corridor parallel to and centred upon the charters towers ravenswood lineament the potential control on gold deposit distribution at the regional to district scale 2 interpret from geological and geophysical data the distribution of pre middle devonian granitoids within these areas that are the preferred host rocks of the payable gold deposits 3 deduce from geophysical data the ene wsw 15 and nnw sse 15 striking structures that cut or bound the intrusions identified in step 2 4 locate segments along the structures identified in step 3 that deviate most from the geometry of a straight line e g potential bends or splays and or intersect other structures or geological contacts or both and 5 define and rank potential targets within the prospective areas identified in step 4 and systematically test the best ones

fluid inclusion geochemistry and 40ar 39ar geochronology constraints on the genesis of the jianchaling au deposit china abstract the giant jianchaling gold deposit is located in the shaanxi province china the mineralization is hosted by wnw trending faults in the mianxian lueyang yangpingguan mly area the mineralization can be divided into three stages based on mineralogical assemblages and crosscutting relationships of mineralized quartz veins these stages from early to late are characterized by the mineral assemblage of 1 quartz coarse grained pyrite pyrrhotite pentlandite dolomite 2 quartz pyrite gold sphalerite galena carbonate arsenopyrite fuchsite and 3 dolomite calcite quartz fine grained pyrite realgar orpiment three types of fluid inclusions have been recognized in this study based on petrographic and microthermometric measurements including pure co 2 and or ch 4 pc type nacl h 2 o w type and nacl co 2 h 2 o c type fluid inclusions these fluid inclusion types are present in quartz from the stage 1 and 2 assemblages whereas the stage 3 quartz only contains w type fluid inclusions the stage 2 assemblage is associated with the mineralization at the jianchaling deposit fluid inclusions of stage 1 quartz homogenize mainly between 250 and 360 c with salinities up to 15 6 wt nacl equiv whereas the stage 3 dolomite with homogenization temperatures of 160 220 c and salinities of 1 1 7 4 wt nacl equiv this indicates that the ore fluid system evolved from co 2 rich probably metamorphic hydrothermal to co 2 poor meteoric fluid all three types of fluid inclusions can be observed in the stage 2 quartz suggesting that this heterogeneous association was trapped from a boiling fluid system these inclusions homogenized at temperatures of 200 250 c and salinities of 1 2 12 4 wt nacl equiv the estimated trapping pressures of the fluid inclusions are between 117 and 354 mpa in stage 1 suggesting an alternating lithostatic hydrostatic fluid system which was controlled by a fault valve at the depth of 12 km two fuchsite samples collected from the stage 2 polymetallic quartz veins yielded well defined 40 ar 39 ar isotopic plateau ages of 197 2 and 194 2 ma and 39 ar 36 ar 40 ar 36 ar normal isochrones of 198 2 and 199 2 ma this indicates that the mineralization at jianchaling is early jurassic ca 198 ma in age we propose that jianchaling is an orogenic gold deposit and formed during continental collision related to the northward subduction of the mian lue oceanic plate during the early jurassic we also conclude that the beginning of the continental collision between the yangtze and the north china cratons took place around 200 ma

nature age and tectonic setting of granitoid hosted orogenic gold deposits of the jiaodong peninsula eastern north china craton china the jiaodong gold province along the southeastern margin of the north china craton has combined production and resources of 900 tonnes of gold more than 95 of the gold in this province is hosted in mesozoic granitoids which intruded late archean metamorphic basement rocks episodically at ca 160 150 and 130 126 ma the deposits of the jiaodong peninsula form one of the largest provinces of granitoid hosted lode gold deposits in the world the jiaodong gold deposits occur as massive auriferous quartz veins hosted in subsidiary second or third order faults and as disseminated and stockwork style mineralization hosted in alteration zones along major regional scale faults mineralization took place during brittle reactivation d3 of pre existing d2 ductile shear zones wall rock alteration is dominated by k feldspar and sericite with also sulfide minerals and extensive silicification closest to the orebodies the alteration was accompanied by the introduction of volatiles fe mg k rb ag as au bi and sb enrichment of base metals in the gold lodes is generally low although locally significant gold deposition took place at temperatures of 250 to 350 c for most gold deposits and the ore fluids are co2 bearing and have calculated salinities of 6 13 wt nacl equiv deposits from the zhao ye xixia and muping rushan belts have similar if not identical structural controls alteration patterns ore mineral assemblages and stable isotope signatures lead isotope data indicate that the ore stage leads were buffered by their host rocks the granitoid hosted gold deposits in the zhao ye belt are most radiogenic the greenstone hosted deposits in the xixia belt is the least radiogenic and the granitoid hosted deposits in the muping rushan belt have intermediate compositions gold mineralization in the zhao ye xixia and muping rushan belts in the jiaodong gold province appears to be broadly contemporaneously at ca 130 120 ma as constrained by shrimp u pb zircon dating on host rocks and a post gold dike as well as by ar ar rb sr and k ar dating of hydrothermal alteration minerals and ores this early cretaceous age is about 100 million years younger than the peak of ultra high pressure metamorphism in the qinling dabie sulu orogen between the north china and yangtze cratons and about 500 km south of the gold province however it overlaps with the extension and exhumation stage of the collisional orogeny and the subduction of the pacific plate beneath the eurasian continental crust whereas the majority of the jiaodong gold deposits occur on the margin of the north china craton some also occur in the suture zone between the two cratons they are significantly landward relative to the subduction zone of the pacific plate compared with typical orogenic lode gold deposits globally lode gold deposits of ca 130 120 ma occurred on both sides of the tan lu fault zone available data favor a temporal link of gold mineralization with pacific plate subduction

shallow subsurface diagenesis of pleistocene periplatform ooze northern bahamas previous studies on early submarine diagenesis of periplatform carbonates have implied that these originally polymineralic aragonite magnesian calcite calcite sediments are susceptible to early diagenesis only in current swept open seaways or where surficially exposed by erosion on the seafloor it has also been proposed that while in the shallow subsurface periplatform oozes retain their original mineralogy for at least 200 000 400 000 yr and remain unlithified for tens of millions of years evidence is reported here for extensive calcitization and selective lithification of periplatform oozes of late pleistocene age in two piston cores collected from water depths of 1 000 m north of little bahama bank it is shown that shallow 30 m subsurface diagenesis can significantly alter the original mineralogy of periplatform oozes to predominantly calcite in less than 440 000 yr and that cementation by calcite can produce chalk ooze sequences within the same time frame periplatform oozes that originally contain a high percentage of bank derived magnesian calcite appear to have a higher diagenetic potential than those originally low in magnesian calcite shallow subsurface calcitization and fithification greatly reduce the diagenetic potential of periplatform carbonates and chalk ooze sequences apparently can persist for tens of millions of years and to burial depths of at least 300 m shallow subsurface diagenesis at water depths 1 000 m proceeds via dissolution of magnesian calcite and aragonite and reprecipitation of calcite as allochem fillings exterior overgrowths and cement it is speculated that density driven kohout convection where seawaters under saturated with respect to magnesian calcite and aragonite and saturated supersaturated with respect to calcite flow through the margins of carbonate platforms is the primary driving mechanism for shallow subsurface diagenesis removal of mg during early stages of deep seafloor and shallow subsurface diagenesis should increase the mg content of interstitial waters which is likely to increase the dolomitizing potential of kohout convection fluid flow

carbonate apron models alternatives to the submarine fan model for paleoenvironmental analysis and hydrocarbon exploration sediment gravity flow deposition along the deep water flanks of carbonate platforms typically does not produce submarine fans rather wedge shaped carbonate aprons develop parallel to the adjacent shelf slope break the major difference between submarine fans and carbonate aprons is a point source with channelized sedimentation on fans versus a line source with sheet flow sedimentation on aprons two types of carbonate aprons may develop along relatively gentle 4 platform margin slopes aprons form immediately adjacent to the shallow water platform and are referred to as carbonate slope aprons along relatively steep 4 15 platform margin slopes redeposited limestones accumulate in a base of slope setting by passing an upper slope via a multitude of small submarine canyons and are referred to as carbonate base of slope aprons both apron types are further subdivided into inner and outer facies belts inner apron sediments consist of thick mud supported conglomerates and megabreccias facies f as well as thick coarse grained turbidites facies a interbedded with subordinate amounts of fine grained peri platform ooze facies g outer apron sediments consist of thinner grain supported conglomerates and turbidites facies a as well as classical turbidites facies c with recognizable bouma divisions interbedded with approximately equal proportions of peri platform ooze facies g seaward aprons grade laterally into basinal facies of thin base cut out carbonate turbidites facies d that are subordinate to peri platform oozes facies g carbonate base of slope aprons grade shelfward into an upper slope facies of fine grained peri platform ooze facies g cut by numerous small canyons that are filled with coarse debris as well as intraformational truncation surfaces which result from submarine sliding in contrast slope aprons grade shelfward immediately into shoal water platform margin facies without an intervening by pass slope the two carbonate apron models presented here offer alternatives to the submarine fan model for paleoenvironmental analysis and hydrocarbon exploration for mass transported carbonate facies

metamorphic origin of ore forming fluids for orogenic gold bearingquartz vein systems in the north american cordillera constraints froma reconnaissance study of δ15n δd and δ18o the western north american cordillera hosts a large number of gold bearing quartz vein systems from the mother lode of southern california through counterparts in british columbia and southeastern alaska to the klondike district in central yukon these vein systems are structurally controlled by major fault zones which are often reactivated terrane bounding sutures that formed in orogens built during accretion and subduction of terranes along the continental margin of north america mineralization ages span mid jurassic to early tertiary and encompass much of the evolution of the cordilleran orogen nitrogen contents and 15n values of hydrothermal micas from veins are between 130 and 3 500 ppm and 1 7 to 5 5 per mil respectively these values are consistent with fluids derived from metamorphic dehydration reactions within the phanerozoic accretion subduction complexes which have 15n values of 1 to 6 per mil the 18o values of gold bearing vein quartz from different locations in the cordillera are between 14 6 and 22 2 per mil but are uniform for individual vein systems the d values of hydrothermal micas are between 110 and 60 per mil ore fluids have calculated 18o values of 8 to 16 per mil and d values of 65 to 10 per mil at an estimated temperature of 300 c d values of ore fluids do not show any latitudinal control these results indicate a deep crustal source for the ore forming fluids most likely of metamorphic origin low dh2o values of 120 to 130 per mil for a hydrous muscovite from the sheba vein in the klondike district reflect secondary exchange between recrystallizing mica and meteoric waters collectively the n h and o isotope compositions of ore related hydrothermal minerals indicate that the formation of these gold bearing veins involved dilute aqueous carbonic and nitrogen bearing fluids that were generated from metamorphic dehydration reactions at deep crustal levels these data are not consistent with either mantle derived fluids or granitoid related magmatic fluids nor do they support a model involving deeply circulated meteoric water

recognition of a cretaceous outlier in northwestern ontario borehole f 88 33 located near rainy river ontario intersected cretaceous nonmarine clastic sediments this is the first documented occurrence in ontario of cretaceous sediments associated with the western interior lithologie and heavy mineral analyses were used to differentiate this unit from the overlying quaternary sediments seventy five species of fossil angiosperm pollen gymnosperm pollen spores megaspores and algal cysts were recovered from borehole f 88 33 and used to date the pre quaternary sediments as late albian to early cenomanian the occurrence of these nonmarine sediments in northwestern ontario helps to better define the limits of cretaceous sedimentation in the western interior

how to resolve the controls on mesothermal vein systems in a goldfield characterized by sparse kinematic information and fault reactivation a structural and graphical approach current mine exposures of auriferous veins in the charters towers goldfield ctgf are characterized by a scarcity of kinematic indicators furthermore the dip direction of exposed and historically mined orebodies largely coincides with the orientation of pre existing discontinuities consequently the reactivation of earlier structures during gold deposition is strongly indicated both factors complicate the structural analysis of the auriferous vein systems as slip on earlier faults likely occurred before new rock failure and evolution of fault networks reflecting the stress field present at the time of gold deposition despite access to drillcore open pits and underground workings extracted data were limited to ten occurrences of wear groove striations and three reverse separations of dykes and a pegmatite cut by sulphide bearing quartz veins because of the scarcity of kinematic information the structural analysis focused on the geometry of veins and ore shoots also applying basic graphical and kinematic methods

carboniferous orogenic gold deposits at pataz eastern andeancordillera peru geological and structural framework paragenesis alteration and 40ar 39ar geochronology the pataz province forms the central part of a 160 km long orogenic gold belt extending along the eastern andean cordillera in northern peru and has produced a total of 6 million ounces moz gold from vein type deposits during the last 100 yr the deposits present several recurrent and typical field characteristics including 1 at a regional scale location of the mineralization in low order structures within a 1 to 5 km wide structural corridor east of a major north northwest striking lineament and in spatial association with the northnorthwest striking margins of the 330 to 327 ma pataz batholith 2 at the mine scale strong lithological controls of the vein geometries and styles the lodes occurring as fairly continuous 5 km long quartz veins inside or along the margins of the batholith or as branching and bedding concordant narrow ore shoots within adjacent folded ordovician turbidite sequences 3 consistent orientations of veins in particular within the batholith where more than 80 percent of the quartz veins are emplaced in north to northwest striking eastdipping brittle ductile deformation zones 4 a consistent au ag as fe pb zn cu sb bi te w metal association and a sulfide rich paragenetic sequence with a first stage composed of milky quartz pyrite arsenopyrite and ankerite and a second stage of blue gray microgranular quartz galena sphalerite chalcopyrite sb sulfosalts electrum and native gold followed by barren calcite dolomite quartz veinlets and 5 hydrothermal alteration of the vein wall rocks consisting of pervasive muscovite alteration with minor chlorite carbonate minerals and pyrite associated with strong bleaching in plutonic rocks and of weak muscovite and chlorite alteration in sedimentary rocks structural analysis of the deposits outlines four synchronous sets of mineralized fractures in the pataz district the predominant north to northwest striking east to northeast dipping system which is generally located in reactivated reverse faults accounts for more than 80 percent of the gold resource of the district three subordinate systems include in decreasing order of economic importance 1 east west striking flat extensional veins 2 bedding concordant veinlets in east west striking and north dipping to north south striking and east dipping limbs of long wavelength folds in ordovician sedimentary rocks and 3 weakly mineralized roughly east west striking sinistral vertical faults the vein orientations of the four structural sets are compatible with a triaxial strain model with the main shortening axis p oriented at 080 15 an intermediate axis oriented at 165 00 and a subvertical extensional t axis oriented at 255 80 under these conditions the richest ore shoots are preferentially sited in sinistral pull aparts which occur at the intersection of either north south striking lodes or extensional lodes with roughly east west striking vertical faults 40ar 39ar dating of the granodiorite monzogranite bodies of the pataz batholith provides good plateau ages at 329 2 1 4 and 328 1 1 2 ma for biotite separates which are similar to a published 329 ma u pb age for the granodiorite a muscovite and a biotite sample from an aplite dike yielded plateau ages at 322 1 2 8 and 325 4 1 4 ma respectively muscovite samples from alteration intimately associated with the gold mineralization yielded three 40ar 39ar spectra with low temperature staircase shaped patterns followed by plateau segments at 314 to 312 ma these ages analytically indistinguishable at the 2 level are considered to be the most probable ages for the mineralization event three other plateaulike ages between 305 and 288 ma have been obtained and are interpreted to reflect partial argon loss during late fluid circulation associated with the intrusion of late cretaceous monzonite porphyries the age determinations are inconsistent with a genetic link between the 314 to 312 ma pataz gold deposits and the 330 to 327 ma calc alkaline pataz batholith or with the 327 to 319 ma aplite dikes or the late cretaceous porphyry magmatism instead the overall homogeneity of the structural mineralogical and geochemical characteristics of the deposits over the 160 km long mineralized belt and the geotectonic evolution suggest that gold mineralization is linked to a large scale thermal event that occurred in a thickened collisional belt undergoing uplift tectonics

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

the role of fluid pressure in the formation of bedding parallel thrust hosted gold deposits sabie pilgrim s rest goldfield eastern transvaal abstract shallowly dipping thrust hosted gold veins occur within the paleoproterozoic transvaal supergroup rocks in the eastern transvaal of south africa internally the veins record episodic events of fluid infiltration and subsequent mineral deposition within discrete local scale thrust faults evidence also exists for subvertical dilation within the individual veins and textures which record open space filling are preserved the probable depth of formation suggests lithostatic pressures in excess of 2 2 kbar and the vein textures indicate numerous reactivation events associated with individual thrust faults occurring in a terrain characterised by low levels of preserved strain fault reactivation may have occurred under conditions of low differential stress in the presence of high pressure fluids with p fluid approaching or exceeding lithostatic levels

geology fluid inclusion geochemistry and 40ar 39ar geochronology of the wulasigou cu deposit and their implications for ore genesis altay xinjiang china abstract the wulasigou cu deposit occurs as veins controlled by a nw trending structure in a devonian volcano sedimentary basin of the altay orogenic belt xinjiang china igneous and sedimentary rocks exposed in the area have undergone greenschist facies metamorphism the ore forming process can be divided into early middle and late stages represented by respectively pyrite quartz polymetallic sulfide quartz and carbonate quartz veins veinlets and or replacement bodies the early veins were deformed and brecciated during a compressional or transpressional event the middle stage veinlets filled fractures in the early stage vein and alteration assemblages and are undeformed suggesting a tensional shear setting the late stage veinlets are mainly open space fissure fillings that cut veins and replacement bodies formed in the earlier stages four types of fluid inclusions fis including aqueous w type mixed carbonic aqueous m type purely carbonic c type and daughter mineral bearing s type have been identified in copper related quartz and calcite from the wulasigou deposit the early stage quartz contains m and w type primary fis that completely homogenized at temperatures of 322 412 c with low salinities of 0 9 6 5 wt nacl equiv in contrast the late stage quartz or calcite contains only the w type fis with homogenization temperatures of 101 234 c and salinities of 0 9 2 9 wt nacl equiv this indicates that the metallogenic system evolved from co 2 rich metamorphic to co 2 poor through input of meteoric fluids all four types of fis can only be observed in the middle stage minerals where they show evidence of vein formation during an episode of fluid immiscibility these fis homogenized at temperatures ranging mainly from 230 to 347 c with salinities clustering 2 7 10 2 wt nacl equiv for the w m and c types and 34 7 38 2 wt nacl equiv for the s type respectively the metal precipitation resulted from a decrease in copper solubility during the fluid immiscibility episode the estimated trapping pressures for the middle stage fluids are 1 55 3 55 kbar suggesting an alternating lithostatic hydrostatic fluid system controlled by fault valve activity at a depth of 13 15 5 km muscovite separates from the middle stage polymetallic quartz veinlets yield a well defined 40 ar 39 ar isotopic plateau age of 219 41 2 10 ma and an 39 ar 36 ar 40 ar 36 ar isochron age of 219 73 2 17 ma this age postdates the final paleo asia ocean closure at ca 250 ma by about 30 ma and indicates that the cu mineralization at wulasigou has occurred in the triassic continental collision setting hence the wulasigou cu deposit may be the first example of orogenic lode cu deposits formed in accretionary orogeny or continental collision

lead isotope systematics and pyrite trace element geochemistry of two granitoid associated mesothermal gold deposits in the southeastern lachlan fold belt

a carbonate submarine fan in a fault controlled basin of the upper jurassic betic cordillera southern spain the middle member of the loma del toril formation kimmeridgian lower tithonian intermediate units betic cordillera consists of up to 250 m of resedimented carbonate material three units have been distinguished the lower unit a is composed of conglomerates that are interpreted as deposited in a major valley on the lower slope of a basin margin unit b calcarenites with some conglomerate intercalation is interpreted as distributary channel deposits and unit c calcarenites as the result of poorly developed depositional lobes of a submarine fan the three units form a recessional sequence they cannot be related to a transgression because the kimmeridgian lower tithonian in the prebetic zone where epicontinental sediments exist is clearly regressive the upper member of the loma del toril formation made up of pelagic limestones with sporadic calcarenites or even thin conglomerate intercalations is best interpreted as a basin plain facies lateral facies relationships suggest that down faulting of the basin floor controlled the development of the fan the scarce occurrence of turbidite beds in the basin plain facies the prevailing channelized facies and the obvious lack of overbank deposits suggest a transport system of low efficiency with fan deposition at the base of slope the underlying jurassic strata cropping out along fault scarps coeval carbonate shelf material and upper slope deposits were the main sources of turbiditic resediments with respect to basin morphology sedimentary processes and fan geometry this jurassic turbidite basin can be compared with the modern california continental borderland ancient analogues have been described by reinhart 1977 and price 1977

nitrogen isotope systematics of mesothermal lode gold deposits metamorphic granitic meteoric water or mantle origin archean gold bearing quartz vein systems constitute one of the most important classes of precious metal deposits however their origin remains controversial mantle granitoid meteoric water and metamorphic related models do not resolve this controversy new n and nitrogen isotope data on hydrothermal muscovite from six gold camps from the late archean superior province of canada and biotite from nine au mineralized locations from the norseman wiluna greenstone belt western australia are reported the majority of muscovites and biotites have n contents of 20 190 ppm and 15 n of 10 20 and 10 70 ppm and 10 24 respectively the 15 n of the mantle is 5 and of granitoids is 0 10 both with generally low n contents organic n is 0 10 meteoric water is 1 9 9 4 and metamorphic rocks are 3 18 increasing with higher grade accordingly the data appear to rule out a mantle hypothesis granitoid related magmatic processes or meteoric water for the deposits but are consistent with ore fluids derived by metamorphic dehydration reactions

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

fluid evolution in the kolar gold field evidence from fluid inclusion studies gold mineralization in the kolar schist belt of the dharwar craton occurs dominantly in the form of a sulfide poor au quartz lode the champion lode exposed in the mysore and other mines and sulfide rich auriferous lodes from the nundydroog mine fluid inclusion microthermometric experiments were conducted on primary inclusions in quartz intimately associated with au mineralization homogenization studies on aqueous biphase l v aqueous polyphase l v halite and aqueous carbonic lco2 vco2 laq inclusions from the champion lode furnish a temperature range of 120 to 420 c freezing of aqueous biphase inclusions and dissolution of halite in the aqueous polyphase inclusions provide salinity of 5 to 50 wt nacl equivalent fluid inclusion thermobarometry from the total homogenization of aqueous carbonic inclusions and from intersecting isochores of coeval pure carbonic lco2 vco2 and pure aqueous inclusions constrain the p t path of evolution of the fluid in the champion lode gold precipitation was likely to have been brought about in response to a sharp fall in pressure with attendant unmixing of liquid co2 from the parent h2o co2 fluid of possible metamorphic origin this would imply transportation of gold by some pressure sensitive complex such as the au carbonyl fluid characteristics are different in the sulfide rich auriferous lodes as indicated by the virtual absence of the co2 bearing and the halite bearing inclusions the fluid evolution path as evident from the crude positive colinearity of temperature and salinity is due to mixing of a low 200 c temperature low saline 7 wt nacl equivalent fluid with a high temperature 400 c high saline 50 wt nacl equivalent fluid the lack of co2 and association of au with sulfides indicate a different mode of gold transport as chloride or bisulfide complexing deposition of which was possibly brought about by fluid mixing

stable isotope o h s c and n systematics of quartz vein systems in the turbidite hosted central and north deborah gold deposits of the bendigo gold field central victoria australia constraints on the origin of ore forming fluids the central and north deborah gold deposits are located in one of 15 mining centers of the bendigo gold field central victoria australia a major world class gold province developed in a turbidite terrane gold mineralization occurs primarily within domes and reverse fault systems in multiply deformed lower ordovician metaturbidites deformation and thrusting occurred between 450 and 420 ma coevally with regional metamorphism at zeolite to greenschist facies in the central and north deborah deposits six stages of quartz veining each with characteristic geometry and mineral paragenesis developed sequentially stages 1 2 and 4 are gold bearing whereas stages 3 5 and 6 are barren gold related quartz veins were deposited at temperatures of 350 25 c based on oxygen isotope geothermometry of silicate phases quartz muscovite and sulfur isotope compositions of coexisting sulfide mineral pairs sphalerite galena this result is consistent with temperatures inferred from fluid inclusions the 18o values of gold bearing vein quartz and coexisting hydrothermal muscovite are uniform within and between the six vein stages ranging from 15 9 to 17 2 per mil and 11 6 to 12 8 per mil respectively the d values of hydrothermal muscovites are also uniform at 68 to 55 per mil ore fluids have calculated 18o values of 8 to 11 per mil and d values of 37 to 17 per mil pyrite of synsedimentary diagenetic origin in slate and sandstone displays sulfur isotope compositions of 23 5 to 8 0 per mil and 0 1 to 11 9 per mil respectively sulfides from gold bearing quartz veins have a range of 7 4 to 8 1 per mil median ca 2 5 the relatively uniform vein pyrites indicate a large uniform sulfur source most likely from desulfidation reactions of sulfide minerals interaction of the ore forming fluid with depleted sulfides at the site of deposition may have shifted the sulfur isotope signatures of source sulfides to more negative values carbon isotope compositions of carbonates range from 5 1 to 9 0 per mil median ca 6 5 nitrogen concentrations and nitrogen isotope compositions of hydrothermal muscovite from quartz veins are 652 to 895 ppm and 2 84 to 4 49 per mil respectively collectively the data define a band in n content vegh rsus 15n coordinate space from higher n and lower 15n in the phanerozoic metasedimenary hosted central and north deborah gold deposits to lower n and higher 15n in predominantly meta igneous hosted neoarchean gold provinces collectively the h o s c and n isotope compositions of ore related hydrothermal minerals indicate that the dilute aqueous carbonic and n bearing ore forming fluids were generated from metamorphic dehydration reactions at deeper crustal levels and were variably influenced by exchange with wall rocks during transport to the site of deposition this genetic model for the central and north deborah gold deposits is consistent with other turbidite hosted lode gold deposits and counterparts in volcanic plutonic terranes in contrast these data are not consistent with either mantle derived fluids or magmatic fluids nor do they support a deeply circulated meteoric surface water model for vein formation

sedimentological and structural evolution of the arabian continental margin in the musandam mountains and dibba zone united arab emirates the northernmost extremity of the oman mountains the musandam peninsula is composed of an allochthonous sequence of permian to middle cretaceous shelf carbonates these are separated from ophiolitic rocks to the south by a northeast southwest trending belt known as the dibba zone this structurally complex belt is composed of allochthonous slope and basin facies sediments haybi volcanic rocks oman exotic limestones sub ophiolitic metamorphic rocks and ultra mafic slices lithofacies correlation confirms that fragmentation and rifting of a vast east facing carbonate platform occurred in middle to late triassic time resulting in the establishment of a shelf edge and small ocean basin this margin was typified from northwest to southeast by ooid skeletal lime sand shoals or small bioherms on the shelf edge a bypass foreslope of well laminated periplatform ooze and basin margin accumulations of carbonate turbidites or debris flows the shelf edge now coincides with the northern boundary of the dibba zone and appears to have remained stationary from middle triassic to late jurassic time periods of arrested carbonate sedimentation on the platform either because of exposure late triassic and middle cretaceous or because of drowning late jurassic are represented in the basin by starved sedimentation and deposition of radiolarian cherts a spectacular platform margin collapse occurred in the middle and late cretaceous as represented by massive conglomerates with clasts as young as albian above an unconformity that progressively removed all of the lower cretaceous the tethyan basinal and ophiolitic rocks of the dibba zone were emplaced from the east southeast during the turonian to lower maastrichtian after emplacement of these allochthonous units compressional deformation in the mid tertiary resulted in large scale open whaleback folds with wavelengths as much as 15 km generally with north south axes in places these folds which affect the complete shelf and allochthonous sequences are overturned toward the west and thrusting has caused previously lower tectonic units of the late cretaceous stacking order to be thrust over previously higher tectonic units thus reversing the late cretaceous tectonostratigraphy the maximum amount of translation on the later thrusts is in excess of 5 km on the hagab thrust where the complete shelf carbonate sequence of the musandam mountains has been thrust west northwest over the previously higher hawasina and haybi thrust sheets the tertiary folding and thrusting can be correlated in time and space with the zagros fold belt of southwestern iran

stratigraphy structure and volcanic hosted mineralization of the mount windsor subprovince north queensland australia the mount windsor subprovince contains a major belt of mineralized cambro ordovician subaqueous volcanogenic rocks at the northern end of the tasman orogenic belt the base of the stratigraphic sequence is a thick continent derived siliciclastic package intruded by alkali andesites typical of intraplate settings this is overlain by massive subaqueous rhyolitic units and then by a mixed association of basaltic andesitic dacitic and rhyolitic volcanics and volcaniclastics containing numerous small elongate pods of quartz hematite or magnetite exhalite the cessation in active volcanism is marked by a change to a sandstone siltstone unit dominated by volcanic sources the majority of volcanics form a coherent group of low to medium k calc alkaline lavas similar to those in modern island arc settings extensional growth faults produced local variation in the stratigraphic thickness the largest growth fault in the area is close to the reward highway and handcuff deposits the sequence has been multiply folded and faulted in the paleozoic but the large scale structure remains relatively simple volcanic hosted massive sulfide vhms deposits occur at the top of the massive rhyolite and in the mixed volcanic package above it with the exception of the reward pyrite pipe the mineralization occurs as blanketlike deposits with low thickness lateral extent ratios the thalanga reward and waterloo deposits are copper rich whereas agincourt magpie liontown handcuff and warrawee are zinc rich and copper poor with a significant barite component

the biostratigraphy of sediments in the volcanic unit of the samail ophiolite sedimentary rocks of pelagic and ocean ridge affinity interbedded with or overlying the volcanic sequence at the top of the oman ophiolite contain datable radiolarian faunas that indicate 1 that the lavas were erupted in an oceanic environment during a narrow time interval ranging from the early cenomanian to the early turonian and 2 that the age progression within this volcanic sequence matches its development from a ridge axis to an off axis setting emplacement of the ophiolite has been dated as late campanian early maestrichtian glennie et al 1974 thus the time gap between formation and emplacement was very narrow

nitrogen distribution in lower palaeozoic slates phyllites of the meguma supergroup nova scotia canada implications for au and zn pb mineralisation and exploration abstract major and trace elements and nitrogen were analysed in 59 cambrian and ordovician slates phyllites of various lithostratigraphic levels within the meguma supergroup 14 ordovician slates phyllites of the ovens gold mineralisation and 16 ordovician slates phyllites of the eastville pb zn cu mineralisation the fixed nitrogen content and the normative n fix k 2 o ratio of muscovite separates members of the goldenville sandstone greywacke quartzite dominated and halifax formation slate phyllite dominated low fixed nitrogen concentration is related to high manganese concentration black slates phyllites of the saddle reef type au mineralisation in the ovens area are characterised by high fixed nitrogen and a high normative n fix k 2 o ratio of muscovite the nitrogen is of secondary hydrothermal origin therefore it might be possible to use the fixed nitrogen as an exploration tool for black slates phyllite hosted gold mineralisation in nova scotia mineralised slates phyllites of the eastville stratabound pb zn mineralisation cannot be distinguished from nonmineralised time equivalent lithologies on the basis of the fixed nitrogen distribution or the n fix k 2 o ratio of muscovite

intrusion hosted mineralization in the charters towers goldfield north queensland new isotopic and fluid inclusion constraints on the timing and origin of the auriferous veins auriferous quartz sulfide veins of the charters towers goldfield are mainly hosted in oxidized i type granitoids of the ravenswood batholith k ar and ar ar isotope age data of hydrothermal muscovite from alteration envelopes of veins at charters towers and the hadleigh castle mine 40 km east of charters towers are indistinguishable within error suggesting broadly synchronous gold deposition between 410 and 404 ma and across a significant segment of the ravenswood batholith published geochronological data indicate that several granitoid bodies were emplaced into the ravenswood batholith at the time of gold mineralization despite their association in space and time with igneous rocks the gold deposits lack an obvious causative intrusion moreover published lead isotope studies indicate that the lead in the ore was not acquired from any of the exposed intrusions a distal origin of the ore forming fluids also may be inferred from nitrogen isotope values of hydrothermal sericite suggesting wall rock interaction with metamorphic fluids or fluids that were in equilibrium with metamorphic rocks during the paragenetic stage of pyrite and arsenopyrite deposition stage ii veins of the charters towers goldfield contain three different types of fluid inclusions which are distinguishable by petrography and microthermometry this study is the first to report saline fluid inclusions in sphalerite 18 9 28 3 wt nacl equiv and vein quartz 20 9 24 7 wt nacl equiv trapped during the stage of gold deposition stage iii the range of temperatures and salinities particularly of the saline inclusions in sphalerite could indicate mixing between hotter more saline fluids e g deep seated magmatic and cooler more dilute solutions e g modified meteoric as the cause of gold deposition the geological and geochemical data are not compatible with derivation of fluids metals and ligands from individual plutons similarity of host rocks ore element associations alteration assemblages structural controls and tectonic settings strongly suggest that the auriferous veins of the charters towers goldfield belong to a group of granitoid hosted lode gold deposits that are generally classified as orogenic

isotope geochemistry and genesis of the liyuan gold deposit shanxi north china abstract the liyuan lode gold deposit is located in the shanxi province central north china craton gold orebodies are mainly hosted in archean metamorphic rocks and structurally controlled by the nne trending faults gold occurs in disseminated and auriferous quartz sulfide veins and veinlets within hydrothermally altered rocks mineralization can be divided into three intervals 1 quartz pyrite stage 2 quartz polymetallic sulfides stage and 3 quartz carbonate stage gold formed mainly in the middle stage sericite sample associated with the middle stage pyrite from phyllic alteration zones yields an well defined 40ar 39ar plateau age of 133 3 1 2 ma which is remarkably consistent with zircon u pb age 133 4 1 1 ma of the quartz porphyry dikes in the liyuan mine indicating a close relationship between gold mineralization and granitic magmatism in the area the sulfur isotopic compositions of pyrite py1 2 from the early stage have a narrow range from 0 3 to 4 1 indicating a deep seated magmatic source however the sulfides py3 5 sphalerite galena from the middle stage have lower 34sv cdt values of 7 2 to 3 0 which is thought to be a result of fluid oxidation during gold mineralization the pb isotopic compositions of sulfides from liyuan ores have 206pb 204pb 207pb 204pb and 208pb 204pb ratios of 16 671 16 860 15 236 15 255 and 41 452 44 159 respectively indicting a high thorium lower continental crust source of ore forming materials the 13cvpdb and 18ovsmow values of late stage calcite ranging from 7 1 to 5 8 and 12 2 to 13 7 respectively illustrating a deep seated magmatic source of carbon bearing portion given the absence of granite bodies at the present mining levels we speculate that the ore forming fluids may have been exsolved from a concealed granite pluton at greater depth based on the regional tectono magmatic events ore geology geochronologic and isotopic data obtained in this study together with the previous published fluid inclusion data we suggest that the liyuan deposit is an orogenic gold deposit that is probably related to the early cretaceous granite magmatism in the interior of the north china craton

a jurassic tongue of the ocean infilled with oolitic sands the belluno trough venetian alps italy abstract the belluno trough is a narrow and elongate basin on the northwestern corner of the apulian plate continental margin it acquired topographic identity in early liassic time during the breakup of a widespread upper triassic carbonate shelf at the beginning liassic the belluno trough was a starved depression accumulating euxinic mudstone and bounded by two shallow water carbonate banks trento and friuli platforms this typical bahamian physiography lasted until late liassic time when the shallow water trento platform collapsed tectonically and suddenly drowned tilting northward and breaking along an old tectonic line it became therefore a submerged pelagic plateau in the meantime the western edge of the friuli platform now the windward margin of an oceanic platform turned into a prolific super producing oolite factory quite soon the oolite sands of the friuli margin started to flow down the slope reaching the basin through numerous entry points and gradually building a complex of coalescent deep sea fans which prograding westward infilled the belluno trough the fans terminated westward against the faulted edge of the trento plateau on which above a karst like surface locally encrusted with manganese red nodular ammonitic limestone was slowly accumulating northward where the topographic relief decreased the oolite fans could spill over the escarpment onto the edge of the plateau by the end of middle jurassic time the belluno trough was no longer a submarine depression but a gentle slope connecting the friuli platform to the deep pelagic trento plateau in callovian time probably because of a short drop in sea level large parts of the friuli platform were exposed to subaerial diagenesis during the subsequent oxfordian transgression the resulting rocky bottom became the substratum for an extensive growth of reefal organisms hydrozoans corals rudists which fringed the friuli platform for the whole malm and cretaceous times

a ductile to brittle shear zone hosted cu mineralization geological geochronological geochemical and fluid inclusion studies of the lingyun cu deposit southern tianshan nw china abstract the lingyun cu deposit is located at the northern margin of the south tianshan accretionary complex nw china in the lingyun mine area the rocks are cut by a nw trending yanxingshan ductile to brittle shear zone all orebodies are hosted in crystal tuff the sulfide mineralization in the lingyun cu deposit can be divided into early e and late l paragenetic stages the e stage is characteristic of fault controlled sulfide assemblages chalcopyrite bornite chalcocite quartz veins in the foliation fabric of the crystal tuff with albite sericite epidote biotite assemblages in the l stage the assemblages of ankerite chalcopyrite bornite chalcocite are present in veinlets that cut the e stage assemblages the sulfide assemblages in the lingyun deposit are characterized by striations in the metamorphosed crystal tuff ribbon like silicate minerals in the crystal tuff share common deformation features with the sulfide assemblages the host rock of the lingyun cu deposit yields a concordia age of ca 405 ma indicating that the aerbishibulake formation formed during southward subduction of the south tianshan ocean beneath the tarim block moreover crystal tuff samples show well developed negative sr anomaly and positive rb th u nd and p anomalies which are common in arc related volcanic rocks the ca 297 ma re os isochron age yielded by sulfides is much younger than the host rock which implies that the lingyun cu deposit is a typical epigenetic deposit both similar ree fractionated patterns between sulfide ores and crystal tuff and the high initial 187 os 188 os ratio 18 54 0 67 indicate significant crustal materials input the 40 ar 39 ar plateau age of ca 292 ma from the ribbon like sericite in crystal tuff is coeval with the mineralization occurrence in the lingyun cu deposit by contrast diorite dikes that crosscut the crystal tuff formed at ca 221 ma which is much younger than the sulfide mineralization thus the mineralization in the lingyun deposit is likely to have been generated by shear zone activity rather than the intrusion of diorite dikes three types of fluid inclusions have been identified in the lingyun cu deposit aqueous w type mixed aqueous carbonic m type and pure carbonic c type inclusions these three types of fluid inclusions are all found in the e stage quartz whereas only the w type fluid inclusions have been observed in l stage ankerite fluid inclusions from the e stage commonly contain co 2 and h 2 o locally with n 2 with low salinity which are common in orogenic deposits by contrast l stage fluid inclusions show low co 2 concentrations and salinity indicating a significant inflow of meteoric water given the regional geology ore geology coeval ore forming and deformation and fluid inclusion features the lingyun cu deposit may be associated with the orogenic class of mineral systems

ore geology fluid inclusion and 40ar 39ar geochronology constraints on the genesis of the yingchengzi gold deposit southern heilongjiang province ne china abstract the yingchengzi gold deposit located at the eastern margin of the zhangguangcai range southern heilongjiang province ne china is the only high grade gold deposit in the region the deposit is hosted in mylonitized paleozoic granite and metavolcanic rocks and is structurally dominated by brittle ductile shear zones and faults the orebodies consist of gold bearing quartz veins and gold bearing altered mylonites the hydrothermal ore forming process can be divided into early middle and late stages characterized by quartz pyrite veins quartz gold polymetallic sulfide veins and quartz carbonate veins or veinlets respectively ore minerals and gold mainly occurred in the middle stage four types of fluid inclusions were identified in the vein minerals based on petrography and laser raman spectroscopy nacl h 2 o w type co 2 h 2 o c type pure co 2 pc type and less common calcite bearing s type inclusions the early stage minerals contain c type and rare pc type fluid inclusions which have homogenization temperatures of 262 400 c and low salinities of 2 20 8 51 wt nacl equiv only the middle stage minerals contain all four types of fluid inclusions with homogenization temperatures of 173 316 c and salinities of 2 20 12 42 wt nacl equiv the late stage quartz and calcite crystals contain only w type fluid inclusions which have homogenization temperatures of 104 207 c and salinities of 1 05 6 58 wt nacl equiv fluid boiling and the mixing caused the rapid precipitation of sulfides and gold these indicate that the ore forming fluid system evolved from co 2 rich metamorphogenic to co 2 poor due to the boiling and input of meteoric water the trapping pressures estimated from c type fluid inclusions are 98 245 mpa in the main ore forming stage giving a reasonable estimate that an alternating lithostatic hydrostatic fluid system controlled a fault valve activity at a depth of 9 10 km 40 ar 39 ar dating of hydrothermal sericite from gold bearing altered rock shows that gold mineralization occurred at 248 ma we assume that the yingchengzi gold deposit was formed in a late permian early triassic continental collision regime following closure of the paleo asian ocean the regional geology ore geology fluid inclusions mineralization age and tectonic setting infer that the yingchengzi gold deposit is a mesozonal orogenic gold system making it the first orogenic gold deposit discovered in the zhangguangcai range ne china

oxygen minimum zone edge effects evidence from the central california coastal upwelling system geologic and biological data from box cores gravity cores and bottom photographs across the modern coastal upwelling system of central california reveal that biogeochemical activity increases along the edges of the oxygen minimum zone omz 0 5 ml 1 o2 macrofauna and benthic foraminifers as well as relative concentrations of calcium carbonate glauconite and fecal pellets all display edge effects the major controls appear to be a combination of dissolved oxygen concentration of near bottom waters bottom currents and possibly bacterially mediated nutrient recycling as well as food supplies omz edge effects should be recognizable in the rock record and may prove to be powerful paleoenvironmental paleoecological indicators

the formation of auriferous quartz sulfide veins in the pataz region northern peru a synthesis of geological mineralogical and geochemical data the pataz region in the eastern part of the north peruvian department la libertad hosts a number of important gold mining districts like la lima el tingo pataz parcoy and buldibuyo economic gold mineralization occurs in quartz sulfide veins at the margin of the calc alkaline pataz batholith that mainly consists of granites granodiorites and monzodiorites the batholith is of paleozoic age and cuts the precambrian to early paleozoic low grade metamorphic basement series its intrusion was controlled by a nnw trending fault of regional importance the gold bearing veins are characterized by a two stage sulfide mineralization bodies of massive pyrite and some arsenopyrite were formed in stage 1 and after subsequent fracturing they served as sites for deposition of gold electrum galena sphalerite and chalcopyrite it is concluded that gold was transported as a aucl 2 complex by oxidizing chloride solutions and deposited near older pyrite by micro scale redox changes and a slight temperature decrease mineralogical textural geochemical and microthermometric features are interpreted as a consequence of mineralization at considerable depth produced by a hydrothermal system linked with the emplacement of the pataz batholith acteristics in order to outline a general physicochemical model of the hydrothermal ore forming processes

quaternary aragonite cycles and oxygen isotope record in bahamian carbonate ooze carbonate ooze in bahamian troughs displays cyclic variation in the content of aragonite a 10 m core devoid of turbidites shows 3 5 cycles each defined by a sharp increase followed by a gradual decrease of aragonite the aragonite curve matches closely the oxygen isotope curve of planktic foraminifera from the same core aragonite highs correspond to light oxygen isotope values and thus to interglacial stages content of terrigenous material is low during interglacials and higher during glacial periods intermittent flooding and exposure of the bahama banks is most probably not the cause of the cycles because the latest increase in aragonite precedes bank flooding by 8 000 yr and because the cycles are distinctly asymmetric with rapid increase and gradual decrease of aragonitic content carbonate dissolution cycles tied to the glacial rhythm of earth9s climate are a more likely explanation of the variations in aragonite content

authigenic dolomite in bahamian peri platform slope sediment authigenic calcium rich dolomite has been discovered in poorly consolidated lower pliocene upper miocene carbonate slope sediments north of little bahama bank the dolomite was recovered from a 5 6 m long piston core that penetrated a slide scar in 600 m of water below an unconformity at 105 cm which extends from the late pleistocene to about the miocene pliocene boundary x ray diffraction data indicate only calcite 85 99 and dolomite as much as 15 and scanning electron microscopy observations indicate in situ precipitation of dolomite stable carbon isotope data indicate a normal open marine source of carbon and oxygen isotope values are consistent with precipitation of both calcite and dolomite from deep cold open marine waters trace element data reveal that dolomitic sediments are depleted in sr 2 and mg 2 relative to nondolomitic upper pleistocene oozes dolomitization occurred in a deep open marine diagenetic environment via whole scale dissolution of aragonite and magnesian calcite and reprecipitation of calcite and dolomite

hydrothermal breccias in vein type ore deposits a review of mechanisms morphology and size distribution abstract breccias are among the most widely distributed rock textures found in hydrothermal vein type deposits previous studies have mainly been interested in developing qualitative descriptive approaches leading to a confusing profusion of terms brecciation originates in numerous ways resulting in highly complex classification systems and frequent misinterpretations of facies field observations are difficult to reconcile with physical theories of fragmentation partly due to the fact that few satisfactory quantitative tools have been developed a review of the main brecciation processes occurring in hydrothermal vein type deposits allows for the discrimination between chemical and physical mechanisms including tectonic comminution wear abrasion two types of fluid assisted brecciation hydraulic and critical volume expansion or reduction impact and collapse each of these mechanisms can be distinguished using nonscalar parameters that describe breccia geometry including fragment morphology size distribution of the fragments fabric and dilation ratio the first two parameters are especially important because 1 the morphology of the fragments allows chemical and physical mechanical breccias to be distinguished and 2 the particle size distribution psd is a function of the energy input during breccia formation the slope of the cumulative psd fractal dimension ranges from high values for high energy brecciation processes to low values for low energy processes indicated by an isometric distribution the evolution of a vein system can be divided into three stages propagation wear and dilation these stages are separated by one threshold of mechanical discontinuity and one of hydraulic continuity these two thresholds also mark the transition between different types of brecciation mineralization occurs during all three stages and may display different textures due to pressure variations the use of quantitative parameters in fault related hydrothermal breccias allows a better understanding of the physical parameters related to a vein environment including structural setting and crustal level as well as fluid rock interactions recognition of the different breccia types could also be important during the early stages of mineral exploration

geologic setting paragenesis and physicochemistry of gold quartz veins hosted by plutonic rocks in the pataz region the pataz region is comprised of different low grade metamorphic proterozoic to early paleozoic basement series overlain by folded late paleozoic to early tertiary sediments and almost undeformed volcaniclastic rocks of late tertiary age the basement is intruded by the pataz batholith along a north northwest trending fracture zone this is the most important intrusive body of the region and consists of a geochemically varied calc alkaline magma suite the pataz batholith hosts numerous auriferous quartz veins with a simple two stage sulfide paragenesis microthermometric measurements indicate that stage i is characterized by medium chlorine k rich fluids probably related to magmatic dewatering stage ii displays medium to high chlorine solutions with significant amounts of na k ca and or mg this fluid composition is consistent with the strong interaction with the host rock as evidenced by the observed alteration features the initial chloride contents of stage ii are similar to those of stage i fluid inclusions further show a wide range of homogenization temperatures that probably reflect tectonically induced changes of pressure native gold with bimodal au ag ratios was found to be related chronologically to the second stage and spatially to pyrite that formed in the first stage as did most of the quartz and some arsenopyrite fractured pyrite was an important control on gold deposition frequently accompanied by galena sphalerite and chalcopyrite there is much evidence that vein formation occurs at considerable depth and is geometrically as well as temporally and genetically linked with the cooling stage of the pataz batholith local physicochemical factors account for quantitative mineralogic differences and for the deposition of either electrum or fine gold with less than 15 wt percent ag the early k bearing chloride solutions appear to be essentially magmatogenic fluids of the gold stage represent either new magmatogenic pulses or solutions recycled in a convective circulation system that included the nearby basement series gold leaching from precambrian to paleozoic country rocks appears appropriate in order to explain the regional distribution of the metal

metallogenesis and fluid evolution of the huangtupo cu zn deposit east tianshan xinjiang nw china constraints from ore geology fluid inclusion geochemistry h o s isotopes and u pb zircon re os chalcopyrite geochronology abstract the recently discovered huangtupo cu zn deposit is located in the dananhu tousuquan arc east tianshan nw china orebodies are hosted in volcano sedimentary rocks of the late ordovician early silurian daliugou formation the metallogenic physicochemistry ore forming fluids and metallogenesis of the deposit were investigated through orebody features fluid inclusion microthermometry laser raman spectroscopy and synchrotron radiation x ray fluorescence srxrf the results indicate that the deposit includes an upper sedimentary exhalative ore belt stage i as well as a lower vein stockwork ore belt in a hydrothermal fluid supply channel stage ii associated with silicification chloritization epidotization pyrophyllitization and beresitization alteration the re os isochron age of 429 5 10 ma obtained from primary chalcopyrite the la icp ms zircon u pb age of 423 3 2 9 ma for the host hangingwall tuff fluid inclusion fi microthermometry and geological characteristics were applied to constrain hydrothermal processes and ore genesis quartz and barite were collected from the massive sulfide and vein ores for fi study four types of fi were identified liquid rich l type vapor rich v type daughter mineral bearing s type and c type containing co2 h2o stage i barite fis yield homogenization temperatures of 232 364 c peak value 265 c with salinities of 4 85 10 94 wt nacl equiv whereas stage ii quartz fis yield temperatures of 270 400 c peak value 350 c with salinities of 2 41 13 72 wt nacl equiv peak value 6 28 wt laser raman spectroscopy analyses of fi gas compositions indicate that the fis contain mainly h2o with minor co2 and n2 initial ore forming fluids comprise a medium high temperature low salinity system of hot evolved seawater that was cooled and diluted by mixing with cold seawater fluid mixing and local boiling would have facilitated mineralization srxrf analyses indicate that the liquid phase is enriched in cu and zn the 34s values of sulfide indicate that the sulfur was derived from the magma host volcanic rocks oxygen and hydrogen isotopic data also imply that the ore forming fluids were mainly derived from deep circulation of seawater and mixed with minor magmatic fluids the estimated trapping pressures for vein stockwork mineralization fluids range from 20 to 60 bar average 40 bar at a depth of 0 4 km the ore fluids ascenting along faults and fracture networks at or near the seafloor played important roles in oreforming processes of the huangtupo vms cu zn deposit

storm effects on siliciclastic and carbonate shelf sediments in the medial silurian succession of pennsylvania abstract upper llandoverian through wenlockian strata in the pennsylvania part of the northern appalachian basin formed on a gentle epeiric ramp that extended from marginal tidal flats through coarser grained mid shelf shoals to a muddy basin center over approximately 10 million years the composition of the accumulating sediment evolved from siliciclastic to carbonate while the ramp maintained a relatively similar configuration and position below sea level and while storm generated processes continued as the major producers of sediment characteristics in both siliciclastic and carbonate parts of the succession sedimentary structures and their sequences are generally similar with only a small number of dissimilar features resulting from the differences in composition small scale coarsening and shallowing upward sequences are present in both mid shelf bar and basin transition deposits although specific sequence characteristics are different in siliciclastic and carbonate parts such sequences record cyclic fluctuations of relative sea level while the composition of the sediment evolved over this extended period the gentle ramp gradient was maintained largely by the processes generated by storms such processes were more effective because of the fluctuations of relative sea level

textures paragenesis and wall rock alteration of lode gold deposits in the charters towers district north queensland implications for the conditions of ore formation ore deposits of the charters towers goldfield ctgf are mainly hosted by fault fill veins extensional 8 of all veins and stockwork like 3 veins are less common and of little economic significance crosscutting relationships and published structural and geochronological data indicate a late silurian to early devonian timing of gold mineralization coincident with regional shortening d4 and i type magmatism paragenetic relationships which are uniform in veins everywhere within the ctgf suggest that vein formation commenced with the deposition of large volumes of buck quartz stage i followed by buck and comb quartz and significant pyrite and arsenopyrite precipitation stage ii gold was introduced during stage iii after earlier sphalerite and coincident with galena and chalcopyrite narrow discontinuous calcite veins of stage iv mark the waning of gold related hydrothermal activity or a later unrelated episode ore zones within the veins are everywhere composed of comb and or gray quartz calcite and or ankerite and bands or clusters of fractured pyrite that are spatially associated with galena sphalerite or chalcopyrite low grade or barren vein sections on the other hand are mainly composed of milky buck quartz with little evidence for modification overprinting or interaction with later fluids gold related hydrothermal wall rock alteration is symmetrically zoned displaying proximal sericite ankerite and distal epidote chlorite hematite assemblages that may be taken to imply wall rock interaction with near neutral fluids ph 5 6 isocon plots assuming immobile al p ti y and zr consistently indicate as k pb s and zn enrichment and na si and sr depletion in altered wall rock specimens relative to the least altered rocks alteration assemblages quartz textures fault rocks and published fluid inclusion and stable isotope data imply that the veins were formed under conditions of episodic fluid overpressuring 0 9 3 8 kbar at a depth of 7 km and a temperature of 310 c the published fluid inclusion data also imply that gold precipitation may have been brought about by fluid mixing however physi and chemisorption of gold complexes onto sulfide surfaces may have been important depositional processes and controls on gold enrichment at the millimeter to centimeter scale given that most gold particles are attached to the surfaces of pyrite crystals of stage ii or to etch pits and fracture surfaces within the earlier pyrite

fluid inclusion and stable isotope study of the shagou ag pb zn deposit luoning henan province china implications for the genesis of an orogenic lode ag pb zn system abstract the shagou deposit located in the eastern qinling orogenic belt central china and hosted by the taihua supergroup is a large sized ag pb zn deposit and has proven reserves of 1 54 million tons of ore with grades of 767 g t ag 13 24 pb and 4 31 zn the ore forming fluids have been previously interpreted as products of direct exsolution of a crystallizing magma or sudden decompression of the fluid exsolved from magma defining the shagou deposit as an intrusion related system in this study the shagou deposit has been identified as an orogenic type mineralization system the hydrothermal ore forming process can be divided into the early quartz pyrite middle quartz polymetallic sulfides and late quartz carbonate stages four types of fluid inclusions in quartz can be distinguished between pc c w and pw types the early and middle stage quartz contains the pc c and w type fluid inclusions while only w and pw type fluid inclusions can be observed in the late stage quartz in the early stage the w type fluid inclusions homogenized at 173 369 c concentrating at 200 240 c with salinities ranging from 5 4 to 8 3 wt nacl equiv but in the middle stage the c and w type fluid inclusions homogenized at 112 313 c concentrating at 180 220 c with salinities ranging from 0 7 to 13 6 wt nacl equiv in the late stage the w type fluid inclusions homogenized at 108 253 c concentrating at 160 200 c with salinities ranging from 2 1 to 8 1 wt nacl equiv the fluids may have experienced a boiling process or fluid mixing in the middle stage the estimated trapping pressures of fluid inclusions in the middle stage ranged from 33 to 211 mpa corresponding to a mineralization depth from 3 3 to 7 7 km for the early stage fluids the calculated 18 o h 2 o and d h 2 o values are 7 5 9 1 96 2 to 110 5 respectively for the middle stage fluids these two values are 1 5 5 3 75 6 to 110 7 but change to 1 0 and 87 for the late stage suggesting an evolution from metamorphic to meteoric in origin in general the shagou ag pb zn deposit is similar in many respects to typical orogenic type mineralization systems

isotope and fluid inclusion geochemistry and genesis of the qiangma gold deposit xiaoqinling gold field qinling orogen china abstract the qiangma gold deposit is hosted in the 1 9 ga taihua supergroup metamorphic rocks in the xiaoqinling terrane qinling orogen on the southern margin of the north china craton the mineralization can be divided as follows quartz pyrite veins early quartz polymetallic sulfide veinlets middle and carbonate quartz veinlets late stages with gold being mainly introduced in the middle stage three types of fluid inclusions were identified based on petrography and laser raman spectroscopy i e pure carbonic carbonic aqueous co 2 h 2 o and aqueous inclusions the early stage quartz contains pure carbonic and co 2 h 2 o inclusions with salinities up to 12 7 wt nacl equiv bulk densities of 0 67 to 0 86 g cm 3 and homogenization temperatures of 280 365 c the early stage is related to h 2 o co 2 n 2 ch 4 fluids with isotopic signatures consistent with a metamorphic origin 18 o water 3 1 to 5 2 d 37 to 73 the middle stage quartz contains all three types of fluid inclusions of which the co 2 h 2 o and aqueous inclusions yield homogenization temperatures of 249 346 c and 230 345 c respectively the co 2 h 2 o inclusions have salinities up to 10 9 wt nacl equiv and bulk densities of 0 70 to 0 98 g cm 3 with vapor bubbles composed of co 2 and n 2 the isotopic ratios 18 o water 2 2 to 3 6 d 47 to 79 suggest that the middle stage fluids were mixed by metamorphic and meteoric fluids in the late stage quartz only the aqueous inclusions are observed which have low salinities 0 9 9 9 wt nacl equiv and low homogenization temperatures 145 223 c the isotopic composition 18 o water 1 9 to 0 5 d 55 to 66 indicates the late stage fluids were mainly meteoric water trapping pressures estimated from co 2 h 2 o inclusions are 100 285 mpa for the middle stage suggesting that gold mineralization mainly occurred at depths of 10 km fluid boiling and mixing caused rapid precipitation of sulfides and native au through boiling and inflow of meteoric water the ore forming fluid system evolved from co 2 rich to co 2 poor in composition and from metamorphic to meteoric as indicated by decreasing 18 o water values from early to late the carbon sulfur and lead isotope compositions suggest the hostrocks within the taihua supergroup to be a significant source of ore metals integrating the data obtained from the studies including regional geology ore geology and fluid inclusion and c h o s pb isotope geochemistry we conclude that the qiangma gold deposit was an orogenic type system formed in the tectonic transition from compression to extension during the jurassic early cretaceous continental collision between the north china and yangtze cratons

sumeini group oman evolution of a mesozoic carbonate slope on a south tethyan continental margin abstract deposition of the mostly mesozoic sumeini group occurred on the slope between the shallow marine arabian carbonate platform and the deep oceanic hawasina basin or south tethys sea these strata record the evolution of the northeast arabian continental margin from permian and triassic rifting to ocean basin closing with the late cretaceous obduction of the semail ophiolite platform margin type and its evolution can be inferred from exposures of these slope sediments at jebel sumeini in the western oman mountains in the lower permian base of the sequence bedded spicular limestones suggest deep marine conditions this is followed by an enigmatic thick sequence of bedded dolomite in the early to middle triassic small carbonate submarine fans formed along a distally steepened slope a subsequent interval of terrigenous clastic sedimentation was followed by development of a steep escarpment margin during ladinian to norian time with coralgal reefs at the shelf break and a debris apron at the base of the scarp the late triassic is marked by another influx of terrigenous sediment which accompanied widespread emergence of the platform in the jurassic a thick apron of thin bedded limestone formed on the slope this apron was cut by channelized gullies that now include blocks of older reefal material and oolitic sands a well documented submergence of the platform during the tithonian and early cretaceous led to the deposition of radiolarian cherts on the slope and basin upper lower cretaceous megabreccias up to 200 m thick suggest an interval of localized slope instability and or tectonism continued deposition of bedded limestone and marl with lesser calcirudite marks the top of stratigraphic sequence at jebel sumeini the early to middle triassic carbonate submarine fan deposits occur as discrete lenticular sequences of bedded calciturbidite modified grain flow and debris flow deposits which were derived from mostly slope sources the ladinian to norian base of slope debris apron deposits were derived from both slope and shallow marine sources including reefs and appear to form a laterally extensive but narrow belt of thick lenticular to sheet like beds of debris which accumulated over a long interval of time coarse limestones in the jurassic gullied slope deposits are distinct in that they occur randomly as individual channelized beds in a sequence dominated by thin bedded lime mudstones thick lower cretaceous megabreccias are distinguished by their great lateral distribution and general lack of matrix

emplacement depth and carbon dioxide rich fluid inclusions in intrusion related gold deposits phanerozoic intrusion related gold deposits have many consistent characteristics such as a spatial temporal and geochemical association with moderately reduced predominantly ilmenite series i type intrusions the deposits exhibit a range of characteristics that vary over a wide range of emplacement depths 7 km deposits in shallow crustal settings 5 km have characteristics of mesothermal environments and are hosted by plutons containing sheeted veins greissen and disseminated gold fluid characteristics also vary with depth deposits in shallow environments contain high temperature 350 c immiscible brine 30 wt nacl equiv and low salinity 5 wt nacl equiv vapor that commonly contains carbon dioxide deposits in deeper environments contain abundant low salinity carbon dioxide rich aqueous fluids 10 wt nacl equiv that in some deposits are postdated by moderate to high salinity brines 10 40 wt nacl equiv these contrasting fluid types are interpreted to be magmatic in origin and are the result of the complex interplay between exsolution of different volatiles carbon dioxide water and chlorine from felsic magmas emplaced at different crustal levels experimental studies have shown that carbon dioxide will exsolve from felsic magmas at much higher pressures than water and chlorine due to its lower solubility in the melt thus deposits formed from felsic magmas in deeper environments will contain abundant carbon dioxide rich fluids subsequent fluids released from the magma are likely to be water rich and more saline felsic magmas in shallow environments will contain lower concentrations of carbon dioxide that will partition into the vapor phase during phase separation between brine and vapor

carbonates and relative changes in sea level abstract in the geologic record some of the most accurate gauges of changes in sea level are the sediment type geometry and diagenesis of carbonate shelves and platforms this is because carbonates frequently occur at or very near sea level and are usually less compacted than siliciclastics world wide changes in relative sea level the sum of eustatic sea level changes sedimentation and crustal movements have occurred repeatedly and cyclicly through geologic time producing characteristic responses in carbonates 1 1 relative rises in sea level usually caused by the cumulative effect of tectonic subsidence and eustatic rise may result in the following 1 1 a drowned carbonate reefs or platforms here carbonate growth potential is exceeded by relative sea level rise and is characterized by shallow water sediments overlain by hardgrounds and or deep water sediments some of which may be condensed sequences 1 2 b platforms where only the fast growing rim and patches of the interior are able to match sea level rise while the remainder of the platform is drowned temporarily 1 3 c platforms which keep up and maintain a flat top at sea level and contain shallow water sediments whose thickness at the least matches the height of the sea level rise if terrigenous supply is limited prograding sheets of shelf carbonate occur frequently capped by supratidal evaporites with prograding shelf margin carbonate clinoforms and turbidites if terrigenous supply is high the shelf carbonates encroach on deltaics 2 2 relative drops in sea level caused by crustal uplift or by subsidence being outpaced by a eustatic drop in sea level cause karst and soil development over shelves and platforms deposition of deep water evaporites in adjacent semi enclosed basins and in open marine basins the deposition of deltaic and aeolian clastics that bypassed the shelf falls are accompanied by platform wide fresh water diagenesis during relative sea level rises marine diagenesis is common in the subtidal portions of the shoaling upward carbonates and fresh water diagenesis and dolomitization and sulphate deposition is common in their intertidal and supratidal portions the stratigraphic significance of these reponses to relative sea level change is that many are tied to eustatic events and so are predictable within a basin of deposition

late albian kiowa skull creek marine transgression lower dakota formation eastern margin of western interior seaway u s a abstract an integrated geochemical sedimentological project is studying the paleoclimatic and paleogeographic characteristics of the mid cretaceous greenhouse world of western north america a critical part of this project required to establish a temporal framework is a stratigraphic study of depositional relationships between the albian cenomanian dakota and the upper albian kiowa formations of the eastern margin of the western interior seaway wis palynostratigraphic and sedimentologic analyses provide criteria for the dakota formation to be divided into three sedimentary sequences bounded by unconformities d0 d1 and d2 that are recognized from western iowa to westernmost kansas the lowest of these sequences defined by unconformities d0 and d1 is entirely upper albian and includes the largely nonmarine basal dakota lower part of the nishnabotna member strata in western iowa and eastern nebraska and the marine kiowa formation to the southwest in kansas the gravel rich fluvial deposits of the basal part of the nishnabotna member of the dakota formation correlate with transgressive marine shales of the kiowa formation this is a critical relationship to establish because of the need to correlate between marine and nonmarine strata that contain both geochronologic and paleoclimatic proxy data the basal gravel facies up to 40 m thick in western iowa aggraded in incised valleys during the late albian kiowa skull creek marine transgression in southeastern nebraska basal gravels intertongue with carbonaceous mudrocks that contain diverse assemblages of late albian palynomorphs including marine dinoflagellates and acritarchs this palynomorph assemblage is characterized by occurrences of palynomorph taxa not known to range above the albian kiowa skull creek depositional cycle elsewhere in the western interior and correlates to the lowest of four generalized palynostratographic units that are comparable to other palynological sequences elsewhere in north america tidal rhythmites in mudrocks at the ash grove cement quarry in louisville cass county nebraska record well developed diurnal and semimonthly tidal cycles and moderately well developed semiannual cycles these tidal rhythmites are interpreted to have accumulated during rising sea level at the head of a paleoestuary that experienced at least occasional mesotidal conditions this scenario places the gravel bearing lower part of the nishnabotna member of the dakota formation in the mouth of an incised valley of an upper albian transgressive systems tract deposited along a tidally influenced coast furthermore it provides a depositional setting consistent with the biostratigraphic correlation of the lower part of the nishnabotna member of the dakota formation to the marine kiowa formation of kansas

resources of gold in phanerozoic epithermal deposits we have estimated earth s endowment of gold in phanerozoic epithermal deposits using a tectonic diffusion model which simulates the emplacement of deposits at a shallow crustal depth and their subsequent vertical tectonic migration in the crust the calculation was calibrated by least squares comparison of a calculated age frequency distribution to the age frequency distribution for 448 epithermal deposits of phanerozoic age results indicate that 17 percent of the epithermal deposits that formed through phanerozoic time remain in the crust today whereas 83 percent have been removed by erosion assuming a similar age distribution for all 1 181 epithermal deposits in our compilation indicates that 307 000 deposits formed throughout phanerozoic time that 63 000 of these remain in the crust and that 244 000 have been eroded grade and tonnage data of gold in 757 epithermal deposits in the compilation have an arithmetic average of 34 7 t and yield an estimate of 2 2 106 t of gold for epithermal deposits remaining in the crust using the model based vertical distribution of deposits remaining in the crust we estimate that epithermal deposits in the upper kilometer of the united states contain 2 9 104 t of gold adjusting for areas of outcropping volcanic rocks in each continent increases our estimate to 4 0 104 t these estimates are similar to the 1 7 104 t gold resource estimated by the u s geological survey using completely different methods several comparisons based on these results provide insights into the efficiency of processes that form epithermal deposits and the outlook for sustainability for instance all of the epithermal deposits that formed through phanerozoic time represent only about 0 03 percent of the gold in the crust only about 0 007 percent of crustal gold remains in epithermal deposits the rest has been eroded and recycled this is consistent with comparisons based on the flux of gold in the taupo volcanic zone which indicate that epithermal deposits trap only 0 1 to 0 2 percent of the gold that moves through convergent margin hydrothermal systems epithermal gold deposits that remain in the crust can supply current production from them for 1 400 to 5 000 years depending on success of exploration and depth of mining finally we are consuming gold from epithermal deposits about 17 000 times faster than earth is replenishing the supply

triassic carbonate submarine fans along the arabian platform margin sumeini group oman the sumeini group formed along the passive continental margin slope that bounded the northeastern edge of the arabian carbonate platform with the initial development of this passive continental margin in oman during early to middle triassic time possibly permian small carbonate submarine fans of the c member of the maqam formation developed along a distally steepened slope the fan deposits occur as several discrete lenticular sequences of genetically related beds of coarsegrained redeposited carbonate calciclastic sediment within a thick interval of basinal lime mudstone and shale repeated pulses of calciclastic sediment were derived from ooid shoals on an adjacent carbonate platform and contain coarser intraclasts eroded from the surrounding slope deposits sediment gravity flows primarily turbidites with lesser debris flows and grain flows transported the coarse sediments to the relatively deep submarine fans channel erosion was a major source of intraformational calcirudite two small submarine fan systems were each recurrently supplied with calciclastic sediment derived from point sources submarine canyons the northern fan system retrogrades and dies out upsection the southern fan system was apparently longer lived calciclastic sediments in it are more prevalent and occur throughout the section the proximal portions of this fan system are dominated by channelized beds of calcirudite which represent inner to mid fan channel complexes the distal portions include mostly lenticular unchannelized beds of calcarenite apparently mid to outer fan lobes carbonate submarine fans appear to be rare in the geological record in comparison with more laterally continuous slope aprons of coarse redeposited sediment the carbonate submarine fans of the c member apparently formed by the funnelling of coarse calciclastic sediment into small submarine canyons which may have developed due to rift and or transform tectonics the alternation of discrete sequences of calciclastic sediment with thick intervals of background sediment resulted from either sea level fluctuations or pulses of tectonic activity

laser 40ar 39ar ages of single detrital white mica grains related to the exhumation of neoproterozoic and late devonian high pressure rocks in the southern urals russia single grains of detrital white mica from two different synorogenic sediments in the southern urals were analysed using the in situ ultraviolet laser ablation ar ar dating technique to discriminate between age signatures associated with a high pressure signal phengites from those related to muscovite only two disparately aged sandstone formations of neoproterozoic upper vendian and upper devonian famennian age were formed by the erosion of high relief source areas with contemporaneously exhumed high pressure rocks a bimodal distribution of ages and chemical compositions can be detected in the two detrital populations there is no age overlap between the two populations reflecting completely different source areas containing high pressure rocks of different ages within the upper vendian sandstones detrital white mica from a 571 609 ma age group is phengitic in composition si 3 3 3 41 per formula unit while an older 645 732 ma age group is comprised of muscovite composition grains only the first group is compatible with the time of late exhumation and emplacement of a source area containing high pressure rocks the neoproterozoic beloretzk terrane the older age range is compatible with a long history of cooling and the allochthonous nature of this terrane detrital white mica from the famennian sandstones zilair formation comprises one age group 342 421 ma containing phengite si 3 21 3 39 per formula unit and muscovite and a second group 446 496 ma containing muscovite only while the derivation of the second group cannot be correlated with any as yet known regional data the first age group indicates the earliest arrival of high pressure rocks at the surface along the suture zone after late devonian arc continent collision

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

evidence for an albian hudson arm connection between the cretaceous western interior seaway of north america and the labrador sea numerous researchers have alluded to the existence of a cretaceous hudson arm connection between the labrador sea and the western interior seaway of north america however the evidence for this marine connection has been circumstantial in this paper we present sedimentary geochemical data that indicate a marine influence in the albian mattagami formation of the moose river basin james bay lowlands ontario the facies associations between dinoflagellate bearing laminated mudstones fluvial sandstones and early pyrite mineralization are interpreted to indicate deposition in the central basin of an estuary we use the facies association between the estuarine fill and coeval kaolinitic paleosols in the moose river basin and in similar deposits in quebec and labrador to reconstruct a southern shoreline of the albian hudson arm to the cretaceous western interior seaway we suggest that development of the hudson arm connection between the labrador sea and the cretaceous western interior seaway may be related to a regional extensional regime associated with rifting between labrador and greenland and the passage of eastern north america over cretaceous hotspots

ore geology and fluid inclusion geochemistry of the tiemurt pb zn cu deposit altay xinjiang china a case study of orogenic type pb zn systems abstract the tiemurt pb zn cu deposit is hosted in a devonian volcanic sedimentary basin of the altay orogenic belt and is thus interpreted to have formed by sea floor hydrothermal exhalation in previous studies our investigation discovered that the deposit is not stratiform or stratabound but structure controlled instead the hydrothermal ore forming process can be divided into the early middle and late stage represented by pyrite quartz polymetallic sulfide quartz and carbonate quartz veinlets respectively the early stage veins and contained minerals are structurally deformed and brecciated suggesting a compressional or transpressional tectonic regime the middle stage veinlets intrude and infill the fissures of the early stage assemblages and show no deformation suggesting a tensional shear setting the late stage veinlets mostly infill open space fissures that crosscut veins and replacements formed in the earlier stages four types of fluid inclusions fis including aqueous type w carbonic aqueous type c pure carbonic type pc and solid bearing type s are identified at the tiemurt deposit the early stage minerals contain the c and w type primary fis that are totally homogenized at temperatures of 330 390 c with low salinities of 0 8 11 9 wt nacl eqv whilst the late stage quartz or calcite contains only the w type fis with homogenization temperatures of 118 205 c and salinities of 1 4 3 4 wt nacl eqv this indicates that the ore fluid system evolved from co2 rich probably metamorphic to co2 poor meteoric fluids and that a significant co2 escape must have occurred all the four types of fis can be only observed in the middle stage minerals and even in a microscopic domain of a crystal representing an association trapped from a boiling fluid system these fis homogenize at temperatures ranging from 270 to 330 c with two salinity clusters of 1 9 14 5 and 37 4 42 4 wt nacl eqv respectively this implies that metal precipitation resulted from fluid boiling co2 escape and transient oversaturation the estimated trapping pressures of fis range from 130 to 380 mpa suggesting an alternating lithostatic hydrostatic fluid system controlled by a fault valve at the depth of 13 km therefore the tiemurt pb zn cu deposit is likely an example of orogenic pb zn cu systems formed in collision orogeny rather than a pre collision vms or sedex system developed in devonian and a new metallogenic model is proposed to interpret the formation of the tiemurt pb zn cu deposit

geodynamic setting of mesothermal gold deposits an association with accretionary tectonic regimes mesothermal gold provinces of phanerozoic age are characteristically associated with regional structures along which allochthonous terranes have been accreted onto continental margins or arcs a recurring sequence of transpressive deformation uplift late kinematic mineralization and shoshonitic magmatism is consistent with thermal reequilibration of tectonically thickened crust mesothermal gold camps in the superior province are spatially associated with large scale structures that have been interpreted as zones of transpressive accretion of individual subprovinces or allochthonous terranes these boundary structures are characterized by the sequence of significant horizontal shortening uplift late kinematic mineralization and shoshonitic lamprophyres and therefore may have the same geodynamic significance as phanerozoic counterparts in this model thermal re equilibration of underplated and subducted oceanic lithosphere and sediments in a transpressive regime over time scales of 10 to 40 m y is a necessary precursor to gold mineralization hydrothermal fluids are released along boundary faults and their splays during uplift the uniform temperature low salinity and mole co2 signify uniform source conditions whereas the variable o c sr and pb isotopic compositions of fluids reflect lithological complexity of the source regions and conduits ou the basis of this model it is suggested that mesothermal lode gold deposits are the product of subduction related crustal underplating and deep late metamorphism rather than magmatic or metamorphic events in the supracrustal rocks secular variations in the generation of archean proterozoic and phanerozoic mesothermal au provinces reflect the timing of collisional orogenies within terranes of these eras

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

oman exotics oceanic carbonate build ups associated with the early stages of continental rifting the so called oman exotic limestones form isolated masses from boulder size to 1 000 m thick of middle to upper permian and upper triassic fossiliferous limestones and crop out within imbricated thrust slices beneath the semail ophiolite in the oman mountains permian exotics are of dominantly reef and forereef facies whereas triassic exotics are more typically of back reef and lagoonal facies they are commonly associated with a substrate of alkalic and transitional tholeiitic basalts and are interpreted as a series of reef associated carbonate buildups deposited in part on oceanic islands or seamounts close to the site of initial rifting of the oman continental margin

petrology of pliocene mississippi river alluvium provenance implications abstractpliocene mississippi river terrace gravels the upland complex crop out east and west of the present mississippi river in the northern mississippi embayment as the only sedimentary unit in the northern mississippi embayment deposited between the end of the eocene and the onset of glaciation its origin provides ground truth about conditions that existed in the heartland of north america within this 30 m yr interval recent studies concluded that the pliocene mississippi river originated in what is now southern canada and that the upland complex is the remnant of a much larger deposit that once extended from canada to the gulf of mexico is there some evidence in the petrology of the upland complex that can confirm this conclusion to determine the provenance of the upland complex we sampled 18 exposures analyzed 50 thin sections and obtained source terrane age data from its zircons upland complex gravel came from proximal early paleozoic carbonate rocks containing bedded and nodular chert

ore forming fluids associated with granite hosted gold mineralization at the sanshandao deposit jiaodong gold province china the sanshandao gold deposit with total resources of more than 60 t of gold is located in the jiaodong gold province the most important gold province of china the deposit is a typical highly fractured and altered disseminated gold system with high grade quartz sulphide vein veinlet stockworks that cut mesozoic granodiorite there are four stages of veins that developed in the following sequence 1 quartz k feldspar sericite 2 quartz pyrite arsenopyrite 3 quartz base metal sulfide and 4 quartz carbonate fluid inclusions in quartz and calcite in vein veinlet stockworks contain c o h fluids of three main types the first type consists of dilute co2 h2o fluids coeval with the early vein stage molar volumes of these co2 h2o fluid inclusions ranging from 50 60 cm3 mol yield estimated minimum trapping pressures of 3 kbar homogenization temperatures obtained mainly from co2 h2o inclusions with lower co2 concentration range from 267 375 c the second inclusion type with a co2 h2o ch4 composition was trapped during the main mineralizing stages these fluids may reflect the co2 h2o fluids that were modified by fluid rock reactions with altered wallrocks isochores for co2 h2o ch4 inclusions with homogenization temperatures ranging from 204 325 c and molar volumes from 55 to 70 cm3 mol provide an estimated minimum trapping pressure of 1 2 kbar the third inclusion type aqueous inclusions trapped in cross cutting microfractures in quartz and randomly in calcite are post mineralization and have homogenization temperatures between 143 228 c and salinities from 0 71 7 86 wt nacl equiv stable isotope data show that the metamorphic fluid contribution is minimal and that ore fluids are of magmatic origin most likely sourced from 120 126 ma mafic to intermediate dikes this is consistent with the carbonic nature of the fluid and the cross cutting nature of those deposits relative to the host mesozoic granitoid

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

the structure of shear related vein type gold deposits a review abstract the structure of vein type gold deposits is defined by the shapes and geometrical relationships of mineralized bodies the form of the mineralization making up these bodies and the sequence of vein forming events most mineralized zones occur within or are spatially associated with shear zones especially shear zones in larger systems of intersecting shear zone sets they range in shape from tabular to linear and in form from disseminated to breccia to stockwork or sheeted veinlet zones to single veins there typically is a complex history of mineral deposition which overlaps and is genetically related to the deformation that generated the host structural zone the purpose of this paper is to consider the structural features of vein type deposits in relation to the geometrical properties and evolution of veinhosting fractures particularly shear zones the evidence indicates that veins are localized by tectonically generated dilatancy in an environment of low mean stress caused by high fluid pressure it is proposed that a major cause of tectonic dilation of shear zones is the interference between intersecting shears during bulk inhomogeneous flattening by movement on systems of intersecting shear zone sets

rb sr k ar and stable isotope evidence for the ages and sources of fluid components of gold bearing quartz veins in the northern sierra nevada foothills metamorphic belt california gold bearing quartz veins occur in and near major fault zones in deformed oceanic and island arc rocks west of the main outcrop of the sierra nevada composite batholith veins typically occupy minor reverse faults that crosscut blueschist to amphibolite grade metamorphic rocks whose metamorphic ages range from early paleozoic to jurassic vein micas and carbonate quartz mica assemblages that formed by hydrothermal metasomatism of ultramafic wall rocks in the alleghany grass valley washington and mother lode districts yield concordant k ar and rb sr ages the dated veins are significantly younger than prograde metamorphism penetrative deformation and accretion of their host rocks to the continental margin new and previously published mineralization ages from 13 localities in the sierra foothills range from about 140 to 110 m y ago with mean and median between 120 and 115 m y the age relations suggest that mineralizing fluids were set in motion by deep magmatic activity related to the resumption of east dipping subduction along the western margin of north america following the late jurassic nevadan collision event co 2 bearing fluids responsible for metasomatism and much of the vein mica carbonate albite and quartz deposition in several northern mines were isotopically heavy delta 18 o asymp 8 14ppm delta d between about 10 and 50ppm and do not resemble seawater magmatic or meteoric waters metasomatic and vein filling mica dolomite magnesite and quartz in altered ultramafic rocks generally formed from fluids with similar sr and o isotope ratios at a given locality consistent quartz mica delta 18 o fractionations delta 18 o sub q m 4 5 4 9ppm from various localities imply uniform equilibration temperatures probably between 300 degrees and 350 degrees c on a local mine scale fluids responsible for both carbonate alteration of mafic and ultramafic wall rocks and albitic alteration of felsic and pelitic rocks had similar sr isotope ratios samples from three veins in the central alleghany district fit a 115 7 or 3 m y rb sr isochron with a 87 sr 86 sr i value of approximately 0 7119 inferred 87 sr 86 sr ratios of metasomatic fluids from mines in different parts of the foothills region vary considerably 0 704 0 718 suggesting that sr was derived from sources ranging from western assemblage mesozoic ophiolitic or arc volcanic rocks to early paleozoic continent derived clastic rocks of the shoo fly complex systematic geographic variations in both sr and o isotopes can be rationalized by assuming extensive fluid interaction with rocks similar to the ones that are exposed within a few kilometers of the veins but the ultimate sources of the fluids and of au and other constituents may be independent of these isotopically lighter meteoric fluids deposited some late quartz overgrowths and occupied secondary fluid inclusions in earlier vein quartz