major types and time space distribution of mesozoic ore deposits in south china and their geodynamic settings the ore deposits of the mesozoic age in south china can be divided into three groups each with different metal associations and spatial distributions and each related to major magmatic events the first event occurred in the late triassic 230 210 ma the second in the mid late jurassic 170 150 ma and the third in the early mid cretaceous 120 80 ma the late triassic magmatic event and associated mineralization is characterized by peraluminous granite related w sn nb ta mineral deposits the triassic ore deposits are considerably disturbed or overprinted by the later jurassic and cretaceous tectono thermal episodes the mid late jurassic magmatic and mineralization events consist of 170 160 ma porphyry skarn cu and pb zn ag vein deposits associated with i type granites and 160 150 ma metaluminous granite related polymetallic w sn deposits the late jurassic metaluminous granite related w sn deposits occur in a ne trending cluster in the interior of south china such as in the nanling area in the early mid cretaceous from about 120 to 80 ma but peaking at 100 90 ma subvolcanic related fe deposits developed and i type calc alkaline granitic intrusions formed porphyry cu mo and porphyry epithermal cu au ag mineral systems whereas s type peraluminous and or metaluminous granitic intrusions formed polymetallic sn deposits these cretaceous mineral deposits cluster in distinct areas and are controlled by pull apart basins along the south china continental margin based on mineral assemblage age and space time distribution of these mineral systems integrated with regional geological data and field observations we suggest that the three magmatic mineralization episodes are the result of distinct geodynamic regimes the triassic peraluminous granites and associated w sn nb ta mineralization formed during post collisional processes involving the south china block the north china craton and the indo china block mostly along the dabie sulu and songma sutures jurassic events were initially related to the shallow oblique subduction of the izanagi plate beneath the eurasian continent at about 175 ma but i type granitoids with porphyry cu and vein type pb zn ag deposits only began to form as a result of the breakup of the subducted plate at 170 160 ma along the nne trending qinzhou hangzhou belt also referred to as qin hang or shi hang belt which is the neoproterozoic suture that amalgamates the yangtze craton and cathaysia block a large subduction slab window is assumed to have formed in the nanling and adjacent areas in the interior of south china triggering the uprise of asthenospheric mantle into the upper crust and leading to the emplacement of metaluminous granitic magma and associated polymetallic w sn mineralization a relatively tectonically quiet period followed between 150 and 135 ma in south china from 135 ma onward the angle of convergence of the izanagi plate changed from oblique to parallel to the coastline resulting in continental extensional tectonics and reactivation of regional scale ne trending faults such as the tan lu fault this widespread extension also promoted the development of ne trending pull apart basins and metamorphic core complexes accompanied by volcanism and the formation of epithermal cu au deposits granite related polymetallic sn w deposits and hydrothermal u deposits between 120 and 80 ma with a peak activity at 100 90 ma

structural features and metallogenesis of the carlin type jinfeng lannigou gold deposit guizhou province china abstract jinfeng previously known as lannigou is the largest carlin type gold deposit in the yunnan guizhou guangxi region in southwestern china gold mineralization in the jinfeng deposit is almost entirely fault hosted and structurally controlled with very little disseminated ore occurring in the adjacent host rocks the structural elements in the jinfeng deposit can be subdivided into 3 groups comprising ns nw and ne striking faults and folds with nw striking structures controlling the overall framework of the deposit four tectonic stages have been recorded in the jinfeng area i e rifting orogenic compression lateral transpression and lithospheric extension a series of contemporaneous normal faults such as the n striking and east dipping f1 and f7 faults developed along the edges of a carbonate platform during basin rifting d 2 t 2 these structures provided an initial framework for subsequent basin evolution and also represent the principal hydrothermal conduits a gradual change of the compression direction during the orogenic stage t 3 from e w to ne sw gave rise to the nw striking structures including large tight to overturned folds such as the huangchanggou synclinorium and associated thrusts such as the f3 fault the development of these orogenic predominantly ne dipping structures as well as accompanying ne striking dextral shear and transform faults such as the f2 fault along the margin of the laizishan dome established the structural pattern of the deposit area the nw striking folds were refolded by ne striking superimposed folds during post collisional lateral transpression j 1 and nw se directed compression oblique stress distribution gave rise to ns trending compression and ew trending extension with dilational zones developing at the intersection of the f2 and the f3 faults east of the laizishan dome it is these dextral and sinistral normal dilational zones in which gold was precipitated during the main ore forming event at jinfeng following the main ore stage lithospheric extension occurred during the yanshan stage j 2 k resulting in minor reverse faults that in places cut pre existing structures the above four main structural deformation stages mirror the evolution of the youjiang basin from inception to basin inversion and post orogenic collapse and renewed extension significant gold metallogenesis at jinfeng occurred during the transition from collisional compression to extensional tectonics in the early jurassic and is focussed into intersections of f2 and f3 and fault splays adjacent to f3 this structurally controlled gold metallogenic model is likely to be applicable to analogous settings elsewhere in the yunnan guizhou guangxi triangle area and has implications for the targeting of carlin type gold mineralization in this region

migration paths and precipitation mechanisms of ore forming fluids at the shuiyindong carlin type gold deposit guizhou china abstract shuiyindong is one of the largest and highest grade stratabound carlin type gold deposits in china this paper reports on the results of petrographic studies electron microprobe analyses empa of arsenian pyrite and the mass transfer during mineralization and alteration and it presents the deposit scale distributions of au as sb hg tl and trace elements in a representative cross section across the shuiyindong carlin type gold deposit guizhou province the main objectives were to identify the precipitation mechanisms of minerals or elements from fluids and the migration paths of ore forming fluids petrographic and empa studies indicate that gold in the primary ores is mainly hosted by arsenian pyrite mass transfer associated with alteration and mineralization shows that au as sb hg tl and s were significantly added to all mineralized rocks fe 2 o 3 and sio 2 were immobile in the main orebodies that are hosted in bioclastic limestone and cao na 2 o sr and li were removed from country rocks the relations between fe and s indicate that the sedimentary rocks at the shuiyindong deposit contain more iron than is needed to combine with all of their contained sulfur to form pyrite this suggests that sulfidation and decarbonation were the principal mechanism of gold precipitation at the shuiyindong deposit hg sb and as commonly formed sulfide minerals such as stibnite realgar and orpiment in late stage quartz calcite veins or absorbed by organic matter in argillite fluid cooling presumably led to depositions of stibnite realgar and orpiment in late stage quartz calcite veins organic matter likely served as a reductant in argillite for the ore fluids causing the precipitation of as sb hg and s as well as au deposit scale distributions of gold and other relevant elements reflect the passage of fluids through the rocks rock strata and structures allowed the ore forming fluids to migrate horizontally along the unconformity surface of the middle upper permian converge on the high position of an anticline and then ascend into the overlying strata along the anticlinal axis the distributions of the major and trace elements show that elements that accompanied the ore forming fluids include au as sb hg tl and s and that na 2 o and li were exhausted in the longtan formation at the anticlinal core during gold mineralization the enrichment of co cr and ni in the longtan formation at the anticlinal core might be associated with deformation that formed the anticline or with gold mineralization different host rocks were preferentially mineralized by different elements the bioclastic limestone is commonly enriched in au whereas the argillite is preferentially enriched in as hg sb and tl the zonation of ore forming elements in the deposit appears to be sb tl as hg au hg as from bottom to top enrichment of au as sb hg and tl provides useful guidance for the exploration for carlin type gold deposits in guizhou anomalies of as and hg in soil or stream sediment might be an important clue and these elements can be used as indicator elements ore forming fluids migrated along the unconformity surface of the middle upper permian and the anticlinal axis so these are favorable sites for exploration for carlin type gold deposits in guizhou

no genetic link between late cretaceous felsic dikes and carlin type au deposits in the youjiang basin southwest china abstract the youjiang basin in southwest china is distinguished by preserving a number of carlin type gold deposits tens of felsic dikes occur in this region and some are present within the ore fields a genetic link between these felsic dikes and ore formation has previously been proposed but detailed field investigation shows that the dikes crosscut the main ore body and clearly postdate gold mineralization three felsic dikes in the youjiang basin have been dated and sims zircon u pb dating results show that the liaotun and xiabaha dikes were emplaced at 97 2 1 1 ma mswd 2 9 and 95 4 2 4 ma mswd 0 56 respectively broadly consistent with a la icp ms zircon u pb age for the bama dike 99 4 0 37 ma mswd 1 4 combined with published dates of the other felsic dikes in this region it is suggested that the felsic magmatic event in the youjiang basin occurred between 100 and 95 ma although a wide range of ages for gold mineralization 275 46 ma has been reported by a variety of methods the best available ages suggest a timing between 235 and 193 direct re os dating on fe sulfides chen et al 2015 re os isochron ages for arsenopyrite from carlin like gold deposits in the yunnan guizhou guangxi golden triangle southwestern china significantly older than the emplacement age of the felsic dikes taken together we conclude that there is no genetic link between these late cretaceous felsic dikes and carlin type au mineralization in the youjiang basin

experimental assessment of two theories for the effect of bedslope on the threshold of bedload transport abstract theoretical analyses for the effect of bed inclination on the threshold of sand transport over submarine slopes and bedforms have not yet been tested with laboratory and field data six hundred and seventy two laboratory experiments are described which determine the threshold velocity u cr for quartz sand on a range of slopes between positive and negative angles of repose the experimental results suggest a marked decrease in threshold velocities on increasingly steeper negative slopes downslope and a general increase for the positive upslope case the results are compared with and support earlier analyses although a marked divergence becomes apparent on slopes which are greater than about 14

vertical flux of biogenic matter during a lagrangian study off the nw spanish continental margin lagrangian experiments with short term drifting sediment traps were conducted during a cruise on rrs charles darwin to the nw coast of spain to study the vertical flux and composition of settling biogenic matter the cruise was split into two legs corresponding to i a period of increased production following an upwelling event on the continental shelf 3 10 august 1998 and ii an evolution of a cold water filament originating from the upwelled water off the shelf 14 19 august the export of particulate organic carbon poc from the upper layer 0 60m on the shelf was 90 240mgc m 2 d 1 and off the shelf was 60 180mgc m 2 d 1 off shelf the poc flux at 200m was 50 60mg m 2 d 1 a modest sedimentation of diatoms 15 30mgc m 2 d 1 after the upwelling was associated with increased vertical flux of chlorophyll a 1 8 2 1mg m 2 d 1 and a decrease of the poc pon molar ratio of the settled material from 9 to 6 4 most of the pico nano and microplankton in the settled material were flagellates diatoms were significant during the on shelf and dinoflagellates during the off shelf leg off shelf the exponential attenuation of poc flux indicated a strong retention capacity of the plankton community between 40 and 75m poc pon ratio of the settled particulate matter decreased with depth and the relative portion of flagellates increased suggesting a novel flagellate and aggregate mediated particulate flux in these waters export of poc from the euphotic layer comprised 14 26 of the integrated primary production per day during the on shelf leg and 25 42 during the off shelf leg which characterises the importance of sedimentation in the organic carbon budget of these waters

a note on negative beach slopes and flow asymmetry abstract an earlier paper proposed an equilibrium model for beach gradients based upon the negative feedback which arises from the gradient s control on the sand transport rate recently published data is here used to examine the model s predictions for the case of negative beach slopes

multiple element mapping and in situ s isotopes of au carrying pyrite of shuiyindong gold deposit southwestern china using nanosims constraints on au sources ore fluids and mineralization processes abstract this study employed high sensitivity and high resolution secondary ionizing mass spectrometry nanosims to determine the distribution of au as cu se and s isotopes of pyrite from the shuiyindong au deposit southwestern china nanosims maps show that au occurs as solid solution and heterogeneously distributes at micron scale in the ore pyrite which is the overgrowth of the preexisting synsedimentary or hydrothermal pyrite core commonly rimmed again by the as and au poor outermost zone there is no detectable au in the synsedimentary pyrite invisible au was observed to fill in the submicron scale cracks of the ore pyrite meanwhile element line profile analysis shows that au occurs in three discrete climaxes in the ore pyrite in situ s isotopic analyses identified two types of s sources the synsedimentary pyrites have large negative 34s values ranging from 38 3 to 18 8 which is a typical biogenetic s generated by bacterial reduction of sea water sulfate the hydrothermal pyrites with zoned texture have a narrow 34s range of 3 5 7 4 with a median of 2 3 similar to the recently published sulfur isotope data of the southwest china s carlin type gold deposits except for the lannigou mine combining the distribution of au and s isotopes in pyrite indicates that the au carrying zones have lower 34s values than that of the ore unrelated zones these nanosims observations indicate that the au mineralization was closely associated with strong deformation of the host rock the au forming the deposit was exotic instead of the reactivated au in the preexisting pyrite formed in the synsedimentary basin the mineralization progress was multistage the distribution of au and s isotopes is hard to interpret by the viewpoint of metamorphic fluid or fluid pressure fluctuation instead it is more consistent with magmatic fluid likely contaminated by sedimentary sulfur during its ascending to the surface in addition the multistage ore formation pattern discovered in this study poses new challenges to determine the mineralization age of the au deposits in southwestern china

sediment flux and equilibrium slopes in a barred nearshore estimates of time integrated values of total itvf and net invf sediment volume flux and the associated changes in bed elevation and local slope were determined for a crescentic outer nearshore bar in kouchibouguac bay new brunswick canada for eight discrete storm events a 100 150 m grid of depth of activity rods spaced at 10 m intervals was used to monitor sediment behaviour on the seaward slope bar crest and landward slope during the storms at which time winds incident waves and near bed oscillatory currents were measured comparisons between storm events and between these events and a longer term synthetic wave climatology were facilitated using hindcast wave parameters strong positive correlations between storm wave conditions significant height and total cumulative energy and total volume flux contrasted strongly with the zero correlation between storm wave conditions and net volume flux itvf values ranged up to 1646 m3 for the experimental grid and were found to have power function relations with significant wave height exponent 2 and cumulative wave energy exponent 0 4 values of invf ranged from 0 up to 100 m3 for the same grid indicating a balance of sediment volume in the bar form through time sediment reactivation increased linearly with decreasing depth across the seaward slope and bar crest reaching maxima of 20 cm for the two largest storms bed elevation and thus slope changes were restricted to the bar crest and upper landward slope with near zero morphological change on the seaward slope the latter represents a steady state equilibrium with null net transport of sediment under shoaling waves measurements of the asymmetry of orbital velocities close to the bed show that the energetics approach to predicting beach slope of inman and bagnold 1963 is sound gradients predicted vary from 0 01 to 0 03 for a range of angles of internal friction appropriate to the local sediment tan o 0 3 0 6 these compare favorably with the measured seaward slope of 0 015 formed under average maximum orbital velocities of 1 12 m s 1 landward and 1 09 m s 1 seaward recorded during the period of the largest storm waves

waves currents sediment flux and morphological response in a barred nearshore system abstract a shore normal array of seven bi directional electromagnetic flowmeters and nine surface piercing continuous resistance wave staffs were deployed across a multiple barred nearshore at wendake beach georgian bay canada and monitored for a complete storm cycle time integrated estimates of total itvf and net invf sediment volume flux together with bed elevation changes were determined using depth of activity rods the three bars ranging in height from 0 10 to 0 40 m accreted during the storm 0 03 m and the troughs were scoured 0 05 m sediment reactivation depths reached 0 14 m and 12 of the nearshore control volume was mobilized however the invf value for the storm was less than 1 of the control volume revealing a near balance in sediment volume in the bar system landward migration of the inner crescentic and second sinuous bars occurred in association with an alongshore migration of the bar form itself the outermost straight shore parallel bar remained fixed in location the surf zone was highly dissipative throughout the storm 3 8 10 2 192 10 2 and the wave spectrum was dominated by energy at the incident frequency spectral peaks at frequencies of the first harmonic and at one quarter that of the incident wave were associated with secondary wave generation just prior to breaking and a standing edge wave respectively the former spectral peak was within the 95 confidence band for the spectrum while the latter contributed not more than 10 to the total energy in the surface elevation spectrum even near the shoreline during the storm wave height exceeded 2 m h s and periods reached 5 s t p k orbital velocities exceeded 0 5 m s 1 u rm s and were above the threshold of motion for the medium to fine sands throughout the storm shore parallel flows in excess of 0 4 m s 1 were recorded with maxima in the troughs and minima just landward of the bar crest the rate and direction of sediment flux is best explained by the interaction of antecedent bed slopes with spatial gradients in the mean and asymmetry of the shore normal velocity field these hydrodynamic parameters represent steady flows superimposed on the dominantly oscillatory motion and assumed a characteristic spatial pattern from the storm peak through the decay period increases spatially in the magnitudes of both the mean flows and flow asymmetries cause an increasing net transport potential erosion decreases in these values spatially cause a decreasing net transport potential and thus deposition these transport potentials are increased or decreased through the gravity potential induced by the local bed slope shore parallel flow was important in explaining sediment flux and morphological change where orbital velocities mean flows and flow asymmetries were at a minimum

magmatic origin for sediment hosted au deposits guizhou province china in situ chemistry and sulfur isotope composition of pyrites shuiyindong and jinfeng deposits

a calibration of the bagnold beach equation abstract a simple sand trap is used to measure swash and backwash bedload transport rates on intertidal profiles data from sixty eight beach experiments are used to calculate a mean value of 12 78 kg m 4 s 2 for the calibration coefficient in the bagnold beach equation

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

sedimentary rock hosted au deposits of the dian qian gui area guizhou and yunnan provinces and guangxi district china abstract sedimentary rock hosted au deposits in the dian qian gui area in southwest china are hosted in paleozoic and early mesozoic sedimentary rocks along the southwest margin of the yangtze south china precambrian craton most deposits have characteristics similar to carlin type au deposits and are spatially associated on a regional scale with deposits of coal sb barite as tl and hg sedimentary rock hosted au deposits are disseminated stratabound and or structurally controlled the deposits have many similar characteristics particularly mineralogy geochemistry host rock and structural control most deposits are associated with structural domes stratabound breccia bodies unconformity surfaces or intense brittle ductile deformation zones such as the youjiang fault system typical characteristics include impure carbonate rock or calcareous and carbonaceous host rock that contains disseminated pyrite marcasite and arsenopyrite usually with m sized au commonly in as rich rims of pyrite and in disseminations late realgar orpiment stibnite and hg minerals are spatially associated with earlier forming sulfide minerals minor base metal sulfides such as galena sphalerite chalcopyrite and pb sb as sulphosalts also are present the rocks locally are silicified and altered to sericite clay illite rocks and or stream sediment geochemical signatures typically include elevated concentrations of as sb hg tl and ba a general lack of igneous rocks in the dian qian gui area implies non pluton related ore forming processes some deposits contain evidence that sources of the metal may have originated in carbonaceous parts of the sedimentary pile or other sedimentary or volcanic horizons this genetic process may be associated with formation and mobilization of petroleum and hg in the region and may also be related to as au and tl bearing coal horizons many deposits also contain textures and features indicative of strong structural control by tectonic domes or shear zones and also suggest syndeformational ore deposition possibly related to the youjiang fault system several sedimentary rock hosted au deposits in the dian qian gui area also are of the red earth type and au grades have been concentrated and enhanced during episodes of deep weathering

an energetics bedload model for a plane sloping beach local transport bagnold s energetics based sediment transport model for streams is used as a basis for the development of a model for the time varying transport of bedload over a plane sloping bed the sediment transport vector is found to consist of two components the velocity induced transport directed parallel to the instantaneous velocity vector and the gravity induced transport vector directed downslope the model is applied to the case of sediment transport within the surf zone for the separate cases of weak and strong longshore currents relative to the wave bore oscillatory water velocity the results suggest the bagnold s oscillatory sediment transport model which forms the basis for a number of longshore sediment transport models is only correct for the special case of weak longshore currents and near normal incident waves for an artibrary strength longshore current v and a local incident wave angle a the longshore transport rate is found to be proportional to sina v 1 sin sup 2 a v sup 3 where u is the wave induced oscillatory water velocity the model also predicts the onshore offshore sediment rate for weak longshore currents and near normal incident waves the predicted equilibrium beach slope is equal to tanf strong longshore currents and or significant local wave angle conditions however cause amore change in this equilibrium beach slope less authors bailard j a inman d l publication date 1981 03 20 osti identifier 6767919 resource type journal article resource relation journal name j geophys res united states journal volume 86 c3 research org scripps institution of oceanography university of california la jolla california 92093 country of publication united states language english subject 58 geosciences shores sedimentation coastal waters gravitation sediments silt velocity water currents currents surface waters 580500 oceanography 1980 1989

sedimentology and morphodynamics of a macrotidal beach pendine sands sw wales abstract the foreshore of pendine sands forms the seaward part of an extensive sandy coastal barrier in a shallow carmarthen bay sw wales the sedimentological features of the macrotidal foreshore reflect a tide induced modification of nearshore wave characteristics as the tide ebbs the breaker height may decrease the surf zone widens and becomes increasingly dissipative and swash backwash velocities diminish a concomitant change from plunging to spilling breakers and increasingly symmetrical swash zone flows are associated with a decreasing beach gradient a zero net transport model demonstrates that the beach profile is self stabilising in the short term and periodic levelling has shown that the beach is in long term equilibrium with prevailing conditions though this does not preclude a significant dynamic response to changing tides and waves the flow regimes of wave generated currents decline as the tide ebbs and normal beach processes do not usually affect the lower foreshore accordingly there is an overall seaward fining of the primary framework component of the sands in more detail this framework component displays a slight seaward coarsening across an upper foreshore dominated by high water swash and surf a rapid seaward fining across the mid foreshore in response to the ebb attenuating swash zone flow velocities and a slight seaward fining across the lower foreshore under the action of nearshore shoaling waves bedforms vary from a swash backwash emplaced flat bed across the upper foreshore to the small ripples of nearshore asymmetric oscillatory flows across the lower foreshore the surface sediment veneer is not representative of the subsurface sediments which form in response partly to fairweather conditions partly to storms the upper foreshore is characterised by swash backwash emplaced plane bedding in fine sands frequently disrupted by bubble cavities the mid foreshore is composed of coarser grained shelly traction clogs arranged as landward and seaward dipping large scale cross bedding and or plane bedding these are probably storm breaker surf deposits the lower foreshore though partially and sometimes totally bioturbated shows landward dipping small scale cross bedding in very fine sands sorted by nearshore shoaling waves tide and storm induced modification of the nearshore flow regimes therefore produces a distinctive shore normal array of sedimentary facies each facies is characterised by diagnostic textural and structural signatures a prograding sequence of such macrotidal deposits would be similar to but more extensive than a comparable microtidal sequence

equilibrium beach profiles under breaking and non breaking waves abstract simple theoretical models to determine the equilibrium profile shape under breaking and non breaking waves are presented for the case of breaking waves it is assumed that the seaward transport in the undertow is locally balanced by a net vertical sedimentation so that no bottom changes occur at equilibrium the parameterization of the water and sediment flux in the surf zone yields a power curve for the equilibrium profile with a power of 2 3 which is in agreement with previous field investigations on surf zone profile shapes three different models were developed to derive the profile shape under non breaking waves namely 1 a variational formulation where the wave energy dissipation in the bottom boundary layer is minimized over the part of the profile affected by non breaking waves 2 an integration of a small scale sediment transport formula over a wave period where the slope conditions that yield zero net transport determine equilibrium and 3 a conceptual formulation of mechanisms for onshore and offshore sediment transport where a balance between the mechanisms defines equilibrium conditions all three models produced equilibrium profile shapes of power type with the power typically in the range 0 15 0 30 comparison with field data supported the results obtained indicating different powers for the equilibrium profile shape under breaking and non breaking waves

metallogenic model of the jinchang au ni deposit in the ailaoshan belt sw china determined on the basis of pyrite trace element contents in situ sulfur isotope composition and pge geochemistry abstract the ailaoshan metallogenic belt in southwestern china contains numerous shear zone related au deposits with au reserves greater than 200 tonnes however the source of ore forming fluids and metals is controversial hampering the construction of genetic models in this study we selected the jinchang au ni deposit in the northern segment of the ailaoshan belt for detailed investigation of pyrite chemistry and in situ sulfur isotope compositions using laser ablation inductively coupled plasma mass spectrometry la icp ms the petrographic and pyrite chemistry analyses revealed four types of hydrothermal pyrite py1 pyrite is euhedral to subhedral and has in situ sulfur isotope 34s values of 5 30 to 6 26 median 2 93 and low concentrations of au ni as sb cu zn pb and ag py1 is interpreted to have formed during the early hydrothermal stage py2 pyrite is subhedral to anhedral and porous with variable size although py2 and py3 show different textural relationships we conclude that both of them formed during the intermediate hydrothermal stage as evidenced by similar sulfur isotope compositions and trace element contents and common intergrowth textures py2 and py3 pyrite have in situ 34s values ranging from 11 6 to 1 29 median 4 45 and relatively elevated concentrations of au ni as sb cu zn pb and ag in py2 and py3 pyrite ni concentrations correlate with co concentration whereas au exhibits moderate positive correlations with ni co and as indicating that au ni and other metals were predominantly sourced from the jinchang ultramafic rocks py4 pyrite is euhedral in shape and has relatively low in situ 34s values of 23 5 to 4 34 median 8 33 the metal concentrations in py4 pyrite are lower than those in py2 and py3 pyrite in general the metal concentrations in the different pyrite populations display systematic changes with low levels in py1 higher levels in py2 andpy3 and low levels again in py4 the average total platinum group element pge concentration of the jinchang ni bearing ultramafic rocks is 26 3 ppb similar to the average value of the primitive mantle of 22 0 ppb the au ni ores from the jinchang deposit have an average pd pt ratio of 5 98 similar to that of hydrothermal ni ores but higher than that of typical magmatic ni ores in contrast the jinchang ultramafic rocks have low pd pt ratios between 0 57 and 1 13 suggesting that the pges in the jinchang intrusion are of magmatic origin similarly the rh ir ratios of au ni ores are consistent with those of hydrothermal ni ores but differ from those of magmatic ni ores the pyrite chemistry in situ sulfur isotope compositions and pge geochemistry suggest that the ore forming fluids and metals associated with the jinchang au ni deposit were dominantly derived from the jinchang ultramafic intrusion mesozoic felsic magmatism or cenozoic regional strike slip activity may have triggered migration of the ore forming fluids leaching of metals from the jinchang intrusion and precipitation of these metals at the boundary between the intrusions and carbonaceous rocks

mineralogy of arsenian pyrites and arsenopyrites of carlin type gold deposits in yunnan guizhou guangxi golden triangle area southwestern china petrographic observations and electron probe micro analysis epma of sulfides from different subclasses of typical carlin type gold deposits in yunnan guizhou guangxi golden triangle area show that both arsenian pyrites and arsenopyrites are major gold bearing minerals gold bearing pyrites are dominated by zoned arsenic pyrites and fine grained euhedral arsenian pyrites zoned arsenian pyrites are characteristics by as poor and s fe rich cores mantled by later formed as rich and s fe poor rims and there is a positive correlation between au and as pyrites with as poor cores have complex origin with some being hydrothermal pyrites precipitated in the early metallogenic stage and the others being syngenetic pyrites altered by hydrothermal fluid core pyrite and rim pyrite were formed in different metallogenic stages the correlation between element contents indicates s was replaced by as in rims the characteristics of multi rims suggest that the hydrothermal fluid acted pulsatorily and the components of hydrothermal fluid varied constantly even if au of some analytical spots from the cores exceeds the detection limit rims can serve as the primary gold bearing location the fine grained euhedral arsenian pyrites with homogeneous texture are similar to the rims of zoned pyrite with characteristics of high as au and low s fe indicating that the as rich mantles of zoned pyrite were probably formed synchronously with the as rich tiny euhedral arsenian pyrite the pyrites from the aggregation of pyrite arsenopyrite are classified into two groups which are of zoned texture and homogeneous texture and have the characteristics of the above two types of pyrites respectively arsenopyrites are subdivided into three generations all having homogeneous texture and belonging to hydrothermal precipitation there are some analytical spots from every generation whose au exceeds the detection limit and whose contents of au as s fe are different insignificantly in different generations indicating they were deposited in the main metallogenic stage the arsenopyrites have higher au abundances than pyrites in the aggregation of pyrite arsenopyrite the precipitation order of gold bearing sulfides is as follows as poor sedimentary pyrites or early metallogenic stage pyrites as rich zoned arsenian pyrites and fine grained euhedral arsenian pyrites arsenopyrites the distribution of au in all types of pyrites and all generations of arsenopyrites is heterogeneous under the resolution of epma microbeam and the homogeneous texture of au map from zoned arsenic pyrites is likely to be a pseudomorph the major modes of occurrence for gold are invisible nanometer size sub microscopic inclusion gold grains with minor ones being invisible lattice gold and visible micrometer size microscopic native gold the gold bearing minerals and the gold modes of occurrence have no essential difference in different subclasses of carlin type gold deposits in yunnan guizhou guangxi golden triangle area suggesting that they had the same ore forming process and setting

uncloaking invisible gold use of nanosims to evaluate gold trace elements and sulfur isotopes in pyrite from carlin type gold deposits one hundred nm resolution secondary ionizing mass spectrometry nanosims was used to determine the distribution of au cu as sb and s and stable isotopes of s 34s 32s in gold bearing pyrite from two refractory carlin type gold deposits west banshee northern carlin trend and turquoise ridge getchell trend located in northern nevada nanosims maps reveal that gold occurs in two discrete episodes in each deposit elevated gold concentrations correlate with elevated concentrations of as sb cu te and lower 34s 32s ratios compared to periods when gold was not deposited precipitation of elevated gold and trace elements at west banshee was followed by precipitation of pyrite with lower gold concentrations whereas at turquoise ridge precipitation of trace element rich pyrite was followed by precipitation of late ore stage minerals these nanosims results are consistent with formation of the deposits by the episodic incursion of gold rich fluids into hydrothermal systems otherwise dominated by gold poor fluids such gold rich fluid pulses may be related to incursions of magmatic fluid which have been shown to have high concentrations of gold arsenic and copper in porphyry and high sulfidation epithermal systems

morphodynamic and experimental assessments of wave theories in intermediate water depths although the near bed wave induced currents predicted by the various wave theories are responsible for seabed sediment transport it is presently unclear which theory should be included in coastal geomorphic models the theoretical expressions for near bed shorenormal flows are re examined and the predictions are tested with morphodynamic and laboratory data five wave theories airy stokes cnoidal solitary and gerstner are summarized here and arranged to predict the maximum onshore and offshore near bed flows and the flow asymmetry as functions of the wave period the wave height and the water depth morphodynamic argument suggests that only stokes and cnoidal wave theories predict the asymmetry required to generate prototype seabed profiles in intermediate water depths laboratory measurements of wave induced near bed flows are then reported and analysed the results suggest that stokes wave theory over predicts the observed peak flows a correction is derived which is shown to be analogous to the pressure attenuation corrections which are routinely applied to wave recording seabed mounted transducer measurements

evaluation of the role of sulfidation in deposition of gold screamer section of the betze post carlin type deposit nevada this study was undertaken to evaluate the relation between sulfidation and gold deposition in the screamer section of the betze post carlin type deposit we also attempted to determine the source of sulfur in the deposit and the possibility that more than one gold depositing event contributed metal to the screamer system gold ore at screamer forms a generally stratiform body hosted largely by the wispy member of the devonian popovich formation and lacks obvious alteration of wall rock gangue minerals gold at screamer is hosted by arsenian pyrite that forms disseminated grains and overgrowths on diagenetic pyrite a strong correlation is observed between the gold content of rock samples and their proportion of ore related arsenian pyrite as determined by point counts isocon plots show that mineralization at screamer involved addition of both sulfur and iron along with gold arsenic antimony tungsten and local silica barium and phosphorus fe al vs s al plots show that most ore samples at screamer do not contain enough sulfur to account for all of their iron as pyrite petrographic examination shows that the iron occurs in pyrite ferroan dolomite and iron bearing micas in order of decreasing abundance the fe al vs s al plots also show that screamer samples with high gold contents contain more pyrite than samples with low gold contents and that samples inside the ore zone have more pyrite than those in the surrounding area these relations are interpreted to indicate that screamer has undergone at least two pyrite forming events the first event which probably took place during diagenesis involved incomplete sulfidation that left some iron in carbonate and silicate minerals the second event which probably took place during gold mineralization sulfidized most remaining iron and added pyrite in the screamer ore zone the 34 s values of chemically extracted sulfur from disseminated pyrite at screamer range from 13 8 to 16 5 per mil and 34 s values for hand picked separates of pyrite and other sulfides in veins cutting these rocks range from 21 2 to 11 7 per mil a significant fraction of samples with high gold contents and of samples in the ore zone regardless of gold content have 34 s values between 1 and 5 per mil these data suggest that early diagenetic sulfur with a wide range of 34 s values was overprinted by sulfur with isotopic compositions in the 1 to 5 per mil range that was associated with gold mineralization the 34 s values for gold related sulfur at screamer are lower than those reported for bulk mineral separates from most other carlin type deposits and from sims analyses of sulfides from the proximal post part of the betze post system and could be magmatic limited evidence can be found for multiple gold forming events in the screamer zone tungsten which might have been introduced by the jurassic age goldstrike stock is widespread in the deposit and correlates closely with gold a few samples with high tungsten gold ratios found along fault zones might be part of an earlier phase of mineralization related to the goldstrike stock a 34 s value for pyrite in one of these samples is similar to the high values reported for sulfides in auriferous polymetallic mineralization in the post section of the deposit but this mineralization is not reported to contain tungsten other veins containing sphalerite have lower 34 s values and lack consistent gold values whereas there is no correlation between gold values and the degree to which the host rocks have undergone sulfidation there is a strong and highly significant correlation between gold values and the abundance of ore related pyrite this shows that simple sulfidation of immediately adjacent wall rock cannot account alone for gold deposition at screamer and it might not be the only ore depositing process in some other carlin deposits a more general extended sulfidation process could be important however one likely process involves mixing of an invading mineralizing fluid containing sulfur and gold with a wall rock fluid containing iron derived from adjacent or distal wall rocks recognition of the source s for this iron and fluid flow pathways responsible for introducing it to the ore zone could provide useful guidance in exploration for the next carlin trend

equilibrium slopes and cross shore velocity asymmetries in a storm dominated barred nearshore system abstract the near bed 0 10 m elevation horizontal velocities were measured across a two barred lacustrine shoreface during a storm and reveal a spatially coherent but temporally variable pattern in the low order moments of the velocity field large cross shore velocity asymmetries indicated 1 1 spatially extensive and temporally persistent offshore mean flows up to 0 18 m s 1 across the landward slope of the linear outer bar reflecting an undertow driven by a wave induced setup 2 2 an onshore directed skewness opposing the mean flow of wind wave origin and persistent under propagating bores in the inner bar system long after this asymmetry had disappeared from the outer bar extensive sediment reactivation with near zero net sediment flux over the whole of the upper shoreface indicated a sediment prism in a steady state volumetrically over the storm cycle uniform depths of sediment reactivation with zero bed elevation change over the storm cycle revealed local slopes in a steady state in the outer linear bar however time integration of the near bed velocity field at this location indicated an offshore net flux of water while sedimentary structures indicated bedform migration and thus at least bedload almost uniformly onshore when ripples and megaripples were present the sediment transport giving rise to the local equilibrium cannot be explained therefore on the basis of the mean properties of the near bed velocity vector but requires knowledge of the time varying instantaneous sediment transport vector onshore migration of the inner bar correlated well with the large and persistent onshore skewness of the velocity distribution in the inner surf zone associated with translatory surf bores throughout the storm decay period low frequency oscillations were only significant close to the shoreline but may have influenced the development of a sinuous three dimensional inner bar form as it migrated onshore

comparison of the native antimony bearing paiting gold deposit guizhou province china with carlin type gold deposits nevada usa the paiting gold deposit guizhou province china has been regarded as a carlin type gold deposit by several researchers alteration and ore related minerals from the paiting deposit were examined and results were compared with the cortez hills carlin type gold deposit nevada usa similarities include the structural and stratigraphic controls on the orebodies in both deposits and the occurrence of invisible gold ionically bound in arsenian pyrite significant differences include the following 1 the gold bearing mineral in nevada is arsenian pyrite however gold bearing minerals in the paiting deposit include arsenopyrite arsenian pyrite and trace pyrrhotite also euhedral or subhedral gold bearing arsenian pyrite at paiting contains significantly less as cu and hg than gold bearing pyrite from nevada 2 alteration in the paiting deposit displays significantly less decarbonatization instead dolomite precipitation which has not been described in nevada deposits is associated with deposition of gold bearing sulfide minerals 3 stibnite and minor native antimony typify paiting late ore stage minerals whereas in nevada realgar orpiment and calcite are common late ore stage minerals precipitation of native antimony in the paiting deposit reflects the evolution of a late ore fluid with unusually low sulfur and oxygen fugacities some characteristics of the paiting gold deposit including formation of ore stage dolomite and precipitation from co2 rich ore fluids at temperatures in excess of 250 c are more typical of orogenic deposits than nevada carlin deposits the presence of similarities in the paiting deposit to both carlin type and orogenic deposits is consistent with formation conditions intermediate to those typical of carlin type and orogenic systems

high grade gold deposition and collapse breccia formation cortez hills carlin type gold deposit nevada usa the cortez hills breccia zone a nevada carlin type gold deposit located in the cortez district on the battle mountain eureka trend formed within a high grade polylithic breccia and grades at the center of the breccia zone are locally in excess of 1 oz ton au sample transects from low grade or below detection 5 ppb to high grade were collected and analyzed using petrography x ray diffraction xrd scanning electron microscopy sem electron probe microanalysis epma and laser ablation inductively coupled plasma mass spectrometry la icp ms analyses to correlate changes in ore pyrite geochemistry and alteration mineralogy with grade and to relate ore deposition to breccia formation ore related minerals textures and analyses are consistent with fluid rock reaction and replacement at relatively low hydrothermal temperatures 260 c during a single heating and cooling event and over a relatively short time frame coincident in time and space with regional magmatism prior to carlin mineralization roberts mountains wenban and horse canyon formations were affected by burial diagenesis and low grade contact metasomatism and metamorphism producing host rocks composed of calcite dolomite and quartz with generally minor dickite pyrite chalcopyrite sphalerite clinochlore tremolite and organic material and minor to trace k feldspar muscovite and biotite acidic ore fluids sulfidized fe in carbonate rock to form rims of au and trace element rich pyrite on earlier formed pyrite or produced small generally 10 m spheres of fuzzy ore pyrite with no apparent core trace elements in ore stage pyrite are dominated by as with strongly correlated hg tl and cu all greater than au lesser and variable sb and minor to undetected ag bi ti w and te ore fluids also variably dissolved calcite and dolomite and replaced carbonate minerals with jasperoid or produced minor pore space ore pyrite and jasperoid after calcite are enclosed in illite that replaced dickite clinochlore and tremolite and filled minor open space primarily between 227 and 277 c for most analyzed samples based on illite chemistry as hydrothermal collapse began ore pyrite chemistry transitioned to an evolved ore stage chemistry with abundant as low to undetected au lesser pb cu sb and diminished hg and tl compared to the ore stage evolved ore stage fluids coincidently precipitated sulfosalt minerals initially unusual cu and hg rich aktashite cu6hg3as4s12 and tl and hg rich christite tlhgass3 and later realgar as cu and zn in hydrothermal fluids and chalcopyrite and sphalerite in the host rocks respectively were consumed calcite only veins indicate termination of the hydrothermal system small fragmented clasts of realgar with chemically distinct au bearing evolved ore stage pyrite rims found in brecciated rock along a faulted dike wenban contact provide the first evidence in a carlin type gold deposit of precipitation of an au bearing pyrite rim on a late ore stage mineral these rare rims likely formed in response to fault movement along the dike wenban contact or by dike injection that allowed deep au bearing fluids to access a higher and cooler part of the system where late ore stage minerals had begun to form these rims further highlight the normal textures in carlin type gold deposits where ore stage pyrite was overgrown by late ore stage sulfosalt minerals demonstrating a single hydrothermal event followed by a single cooling event this paragenesis is consistent with previously modeled deposit formation time frames of 45 000 to 15 000 years two styles of breccia were identified within the deposit replacement matrix supported breccia in which an illite rich punky matrix encloses au bearing pyrite jasperoid and variable relict calcite formed during intense ore stage alteration and mineralization the fine grained ore and alteration replacement minerals did not require significant open space to form later evolved and late ore stage sulfosalt minerals and calcite that are visible at the hand sample scale provide the earliest evidence for the development of significant open space hydrothermal collapse allowed the incursion of cooler meteoric water into the system which along with the retrograde solubility of calcite provided coupled mechanisms driving significant calcite dissolution collapse brecciation and formation of the cortez hills breccia zone dissolution and collapse brecciation increasingly concentrated ore stage pyrite as the hydrothermal system transitioned to the late ore stage contributing to high au grades

sulfur isotope and trace element compositions of pyrite determined by nanosims and la icp ms new constraints on the genesis of the shuiyindong carlin like gold deposit in sw china the shuiyindong carlin like gold deposit the largest one of this type in china is located in the late paleozoic early mesozoic youjiang basin the pyrites in the studied ore bodies no i to v can be divided into four main types plus several sub types 1 as poor pyrites include py1 py1a and py1b py2 and py3 and 2 as rich pyrite py4 py4a and py4b in situ la icp ms analyses show that the as rich pyrite also contains higher au cu sb and tl than the other pyrite types in situ nanosims analyses show the 34s variation of py1 48 1 67 5 py2 2 4 7 6 py3 9 2 14 2 and py4 3 0 6 6 with the average values of 58 1 5 1 11 4 and 3 1 respectively the large 34s variations of as poor pyrites may reflect a sedimentary source however the narrow ranges of 34s values for the as rich pyrite py4 may not reflect a sedimentary but a magmatic or metamorphic origin a metamorphic sulfur source of py4 is favored due to paucity of coeval magmatism in the region and decreasing variations of 34s values from py1 to py4 integrated transmission electron microscope tem and nanosims element mapping show that the distribution and concentration of au are discordant with as and cu at the submicron scale also implied by the occurrence of some of au as nano submicron particles in py4 overall our new data indicate that the ore fluids were not only enriched in au but also in as cu and s taking an alternative of fluid oxidation probably resulting in the decreasing 34s values of py4 our result of i to v orebodies indicates the mixing between the underlying metamorphic fluid and meteoric water integrated variations in 34s and as au cu correlations across individual pyrite grains infer the physicochemical changes of aqueous and or aqueous carbonic fluids along migration paths