east asian monsoon variations during oxygen isotope stage 5 evidence from the northwestern margin of the chinese loess plateau abstract we present the results of high resolution multi proxy climate studies of the s1 palaeosol corresponding to oxygen isotope stage ois 5 from the northwestern margin of the chinese loess plateau area here s1 is much thicker ca 6 8 m than in the central loess plateau areas ca 2 m where most previous studies have been conducted hence much higher resolution stratigraphic studies are possible yielding more insight into the temporal variations of the east asian monsoon during mis 5 the frequency dependent magnetic susceptibility as well as the concentration of secondary carbonate is used as an indicator of the summer monsoon intensity and the median particle size as an indicator of the winter monsoon intensity the results suggest that the northwestern margin of the chinese loess plateau experienced the strongest summer monsoon intensity in sub stage oiss 5e and the weakest in oiss 5a among the three warmer periods during stage 5 the summer monsoon was weaker in oiss 5b than in oiss 5d a dusty interval interrupted the second warmer period 5c and a soil forming event interrupted the first colder period 5d the results also suggest that the directions of changes in the intensities of summer and winter monsoons may not always have been proportionately opposite for example the weakest summer monsoon occurred in oiss 5a during which the winter monsoon was not the strongest we further conclude that the winter monsoon during the last interglacial was probably driven by global ice volume fluctuations while the summer monsoon was primarily controlled by the northern hemisphere solar insolation and was probably modified by a feedback mechanism that is the climatic buffering effect of low latitudinal oceans may have distorted the response of the summer monsoon to insolation variations finally our results do not show the degree of climatic instability comparable to that recorded in the grip ice core for the last interglacial oiss 5e even though the study area is situated in a region which has been sensitive to climatic changes

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

sediment hosted disseminated gold mineralisation at zarshuran nw iran mineralisation at the zarshuran nw iran occurs on the flank of an inlier of precambrian rocks hosted in black silty calcareous and carbonaceous shale with interbedded dolomite and limestone varying in thickness from 5 to 60 m and extending along strike for approximately 5 6 km two major steeply dipping sets of faults with distinct trends occur in the zarshuran 1 northwest 310 325 and 2 southwest 255 265 the main arsenic mineralisation occurs at the intersection of these faults the mineral assemblage includes micron to angstrom size gold orpiment realgar stibnite getchellite cinnabar thallium minerals barite au as bearing pyrite base metal sulphides and sulphosalts hydrothermal alteration features are developed in black shale and limestone around the mineralisation types of alteration include 1 decalcification 2 silicification 3 argillisation 4 dolomitisation 5 oxidation and acid leaching and 6 supergene alteration the early stage of mineralisation involved removal of carbonates from the host rocks followed by quartz precipitation the main stage includes massive silicification associated with argillic alteration in the late stage veining became more dominant and the main arsenic ore was deposited along fault cross cuts and gouge these characteristics are typical of carlin type sediment hosted disseminated gold deposits the early stage of mineralisation contains only two phase aqueous fluid inclusions the main stage has two groups of three phase co2 bearing inclusions with minor ch4 n2 associated with high temperature two phase aqueous inclusions during the late stage fluids exhibit a wide range in composition salinity and temperature and ch4 becomes the dominant carbonic fluid with minor co2 associated with a variety of two phase aqueous fluid inclusions the characteristics of fluids at the zarshuran imply the presence of at least two separate fluids during mineralisation the intersections of coexisting carbonic and aqueous inclusion isochores together with stratigraphic and mineral stability evidence indicate that mineralisation occurred at 945 445 bar and 243 59 c implying a depth for mineralisation of at least 3 8 1 8 km assuming a lithostatic pressure gradient fluid density fluctuations and the inferred depth of formation suggest that the mineralisation occurred at the transition between overpressured and normally pressured regimes geochronologic studies utilising k ar and ar ar techniques on hydrothermal argillic alteration whole rock and separated clay size fractions and on volcanic rocks indicates that mineralisation at zarshuran formed at 14 2 0 4 ma and was contemporaneous with nearby miocene volcanic activity 13 7 2 9 ma it is proposed that mineralisation was the result of the infiltration of hydrothermal fluids containing a magmatic gas component and that it was localised in the zarshuran unit because of the redox boundary that it provided and or because it lay between an overpressured region at depth and a zone of circulating hydrostatically pressured fluids above

mineral paragenesis alteration and geochemistry of the two types of gold ore and the host rocks from the carlin type deposits in the southern part of the goldstrike property northern nevada implications for sources of ore forming elements ore genesis and mineral exploration this study was undertaken to characterize the mineral paragenesis and metal zoning at the property scale evaluate the potential sources of ore related metals quantify the relationship between intensity of alteration and gold grade and propose a comprehensive genetic model for the carlin type au deposits at the southern part of the goldstrike property nevada mineralogy textural relationships whole rock composition and spatial distribution of the studied samples revealed two types of gold ore ore i and ii the former which is hosted by the roberts mountains and rodeo creek formations and the wispy planar and upper mud units of the popovich formation is the most abundant and widespread in the property ore i is characterized by intense hydrothermal alteration e g carbonate dissolution silicification and precipitation of pyrite and high amounts of trace elements e g ag as au ba cd cu hg mo ni s sb se te tl and zn on the other hand ore ii which is hosted in the wispy planar and soft sediment deformation units of the popovich formation is mainly confined to the central north northwest portion of the screamer deposit and is weakly altered with low concentration of trace elements both ores i and ii contain similar average concentrations of au in whole rock 14 and 19 g t au respectively and in pyrite 290 and 540 ppm respectively however auriferous pyrite from ore i has higher trace element as ag cu hg ni sb se and tl au ratios than ore ii the sedimentary units are interpreted to be the major local source of cd mo ni u v and zn and minor as cu hg and se as denoted by the composition of least altered samples and diagenetic pyrite and sphalerite this study reveals that al2o3 and tio2 are the most immobile compounds and their distribution indicates a homogeneous source for the detrital components in the sedimentary rocks among the ore related trace elements tl best correlates with au grade r 2 0 69 and shows some relationship with the calculated amount of pyrite r 2 0 49 indicating that tl would be the best element to vector toward zones of high grade carlin type au mineralization gold grades do not correlate with the amount of pyrite degree of alteration or organic c our results integrated with available thermodynamic data for au ore related elements and sio2 lead us to suggest that the formation of ore i occurred more proximal to the major mineralizing conduits as the hot more acid sio2 and trace element rich auriferous fluids interacted with fe bearing impure carbonate host rocks intensely dissolving the carbonate rocks and precipitating quartz and auriferous pyrite in the betze post and rodeo deposits as the fluids moved laterally throughout the favorable host rocks the ph increased leading to a decreasing in the rate of carbonate dissolution and in the solubility of silica favoring the formation of more distal ore ii in the central northern part of the screamer deposit significantly the gold concentrations in whole rock and in pyrite are in some way very similar in both ore types being slightly higher in ore ii suggesting that less acidic conditions were still favorable for the incorporation of gold in the structure of pyrite even at lower concentrations of other trace elements

alteration associated with gold deposition at the getchell carlin type gold deposit north central nevada wall rock alteration at the getchell underground deposit was examined to determine the effects of au bear ing fluids on host lithologies and the relationship between k bearing alteration minerals and au deposition the major minor and trace element geochemistry of highly altered and mineralized to unmineralized rocks from the getchell deposit was quantified for more than 50 samples collected along 13 transects through calcareous siltstone and carbonaceous limestone and along one transect through a rhyodacite dike each transect in sedimentary rocks was collected along a single homogeneous bed that could be followed from high grade ore to moderately altered rock or waste rock analyses were obtained for 39 elements 10 oxides and loss on ignition using multiple techniques petrographic studies were integrated with geochemistry and x ray diffraction and electron microbeam analyses to identify ore and alteration minerals and to correlate mineralogy with geochemical fluxes geochemical analyses indicate that ti al zr and th behave as immobile elements immobility isocon diagrams show that significant hg sb se te tl and cs are typically added to the wall rocks with au fe is im mobile in some transects added to wall rocks in others and removed from rhyodacite host rocks minor s and w are usually added to the rock whereas minor cu and mo are variably added or removed sio 2 appears to be either added during alteration or remain constant elements that are consistently removed during alteration include ca mn sr and sc and minor mg ba and k na was significantly removed from the rhyodacite au correlates positively with ag hg sb se si te and tl and negatively with ca mn and sc element fluxes correspond with observations of mineral abundances and show that sulfidation and decar bonitization are spatially associated with gold mineralization au hg sb tl cu and possibly te and w were incorporated in trace element rich pyrite as host rock fe was sulfidized fe was added to mineralized rocks in some transects indicating that pyritization occurred in addition to sulfidation cs is a component of galkhaite a trace mineral that is relatively common in some parts of the getchell system decarbonitization removed as much as 95 wt percent calcite from mineralized rocks in some transects and is responsible for loss of ca mn sr and sc although sio 2 as and s are significantly added to carlin type systems they do not appear as major added components in the isocon diagrams this is because the halos for these components are much larger than the areas examined by the sample transects x ray diffraction analyses identified minerals in ore and waste samples and quantified clay minerals including illite and montmorillonite kaolinite was not identified or is present in low abundances in both mineralized and unmineralized rocks montmorillonite does not correlate with gold and textures are consistent with pore filling deposition of montmorillonite following au deposition illite abundance exhibits a positive correlation with au r 2 0 80 intergrowths of illite with ore stage pyrite support a genetic relationship between the two minerals and indicate that illite formed as part of the au related hydrothermal event mineral abundances and textures suggest that illite formed by alteration of k feldspar during au deposition results show that dating of k bearing phases in sedimentary rocks other than illite would provide ages unrelated to gold deposition

the long canyon deposit anatomy of a new off trend sedimentary rock hosted gold discovery in northeastern nevada the long canyon deposit is a new sedimentary rock hosted gold discovery located in northeastern nevada over 150 km east of the well explored carlin trend unlike most examples of this type the deposit is hosted in a sequence of cambro ordovician carbonate rocks deposited in a periodically emergent platform to shelf edge environment the strata were strongly deformed and weakly metamorphosed during a mid mesozoic orogenic event that segmented and extended a brittle 80 m thick dolomite layer into a series of elongate n to ne trending boudin blocks while the enclosing limestone underwent ductile deformation this unusual structural architecture focused subsequent contractional deformation as well as tertiary extensional brittle deformation forming pathways for meteoric and hydrothermal fluids which formed and enlarged dissolution cavities and dissolution breccias along boudin margins boudin necks and normal faults gold occurs primarily in zones of polyphase dissolution breccias that are localized in minor faults and fold hinges in the structurally complex areas along and adjacent to dolomite block margins two general phases of brecciation are present including calcareous breccias and later fe as oxide rich breccias which carry the highest gold grades breccias are accompanied by variable pervasive silicification alteration assemblages include zoned dickite white mica hematite in the cores of mineralized zones with peripheral kaolinite sericite and goethite hematite and ultimately more distal illite smectite local preservation of fine grained sulfides encapsulated in calcite and silica suggests that the iron oxide assemblages may represent oxidation of fine grained pyrite marcasite arsenopyrite assemblages as currently defined the long canyon deposit extends for 3 km in a northeasterly direction and consists of several subparallel zones of mineralization focused on boudin block margins boudin necks and incipient boudins it contains a combined measured indicated and inferred estimated resource comprising 2 2 million ounces of gold at an average grade of 2 3 g t gold metallurgical work indicates that the deposit is highly amenable to cyanidation by heap leaching or milling the long canyon deposit is open to further exploration and resource additions and is shallowly buried relatively high grade and thoroughly oxidized the stratigraphic position of the long canyon deposit on the paleozoic shelf and its location well east of the majority of identified major trends indicate significant potential for new discoveries in this underexplored area of eastern nevada

age constraints on jerritt canyon and other carlin type gold deposits in the western united states relationship to mid tertiary extension and magmatism carlin type gold deposits are difficult to date and a wide range of ages has been reported for individual deposits therefore several methods were employed to constrain the age of the gold deposits in the jerritt canyon district dated igneous rocks with well documented crosscutting relationships to ore provided the most reliable constraints k ar and 40 ar 39 ar dates on igneous rocks are as follows andesite dikes 324 ma sericitic alteration in andesite dikes 118 ma basalt dikes 40 8 ma quartz monzonite dikes 39 2 ma and calc alkaline ignimbrites 43 1 to 40 1 ma of these only the andesite and basalt dikes are clearly altered and mineralized the gold deposits are therefore younger than the 40 8 ma basalt dikes the sericitic alteration in the andesite dikes is unrelated to the gold deposits a number of dating techniques did not work k ar and 40 ar 39 ar dates on mica from mineralized ordovician to devonian sedimentary rocks gave misleading results the youngest date of 149 ma from the smallest 187 os 188 os initial 0 9 3 6 but did not yield a meaningful isochron due to very low re and os concentrations and large analytical uncertainties paleomagnetic dating techniques failed because the hydrothermal fluids sulfidized nearly all of the iron in the host rocks leaving no remnant magnetism when published isotopic dates from other carlin type deposits in nevada and utah are subject to the rigorous evaluation developed for the jerritt canyon study most deposits can be shown to have formed between 42 and 30 ma k ar and 40 ar 39 ar dates on the youngest preore igneous rocks range from 41 to 32 ma whereas the oldest postore igneous rocks range from 35 to 33 ma hydrothermal adularia from the twin creeks deposit yields similar 40 ar 39 ar dates of 42 ma k ar dates on supergene alunite range from 4 to 30 ma k ar and 40 ar 39 ar dates on micas separated from sedimentary 395 43 ma and igneous 145 38 ma rocks are usually much older than the gold deposits and most are suspect because they are from incompletely reset preore micas or from mixtures of preore and ore stage mica fission track dates on zircons are also generally older than the deposits 169 35 ma and are not completely reset by mineralization apatites are likley to be reset by the hydrothermal systems and by younger thermal events and yield dates 83 22 ma that are younger than those from zircon independent support of a mid tertiary age is provided by the low delta d sub h 2 o values of hydrothermal fluids from 10 widely separated carlin type deposits 134 or 23ppm the low delta d sub h 2 o values are consistent with a mid tertiary age when the climate was cool but are inconsistent with the cretaceous and jurassic ages favored by some workers when the climate was warm the age and distribution of carlin type deposits coincides with areas that underwent extension and calc alkaline magmatism over the same time period despite this relationship the deposits lack clear spatial or genetic relationships to mid tertiary epizonal plutons rather many deposits are localized along preexisting crustal fault zones in the getchell trend structures tapped deep sourced metamorphic or magmatic fluids and subsequently variably exchanged meteoric water in the other trends and districts only variably exchanged meteoric water has been detected these relationships suggest either that all of the deposits formed from deep sourced fluids and were subsequently flooded by meteoric water or that fluids from different sources evolved to produce deposits with similar charateristics

refined insight into 40ar 39ar progressive crushing technique from k cl ar correlations in fluid inclusions abstract hydrothermal fluid activity associated with geological processes can now be dated by 40ar 39ar progressive crushing of minerals thanks to recent advances in high precision mass spectrometry however methods of data analysis and interpretation for these high resolution measurements still need to be refined in this study we report further insights into using k cl ar diagrams as tools for interpreting ages of secondary and primary fluids from 40ar 39ar stepwise crushing experiments three paragenetic mineral pairs of muscovite and wolframites from a southern china tungsten deposit were investigated using the 40ar 39ar technique through laser incremental heating and progressive crushing of single minerals incremental heating analyses of muscovites yielded flat age spectra defining plateau ages of 156 153 ma progressive crushing experiments of wolframites yielded anomalously old apparent ages due to excess 40ar however the apparent ages decline quickly after the initial steps and stabilize to form age plateaus of 156 153 ma without excess 40ar the plateau age steps interpreted as ages of gases derived from primary fluid inclusions pfis yield well defined isochrons with ages ranging from 157 to 153 ma and initial 40ar 36ar values that are indistinguishable from the modern atmospheric value digitally created 2d and 3d diagrams of k cl ar correlations can easily reveal distribution trends and correlation planes from the crushing steps interpretations of these diagrams further reveal the ages of secondary fluid inclusions sfis 87 to 83 ma and primary fluid inclusions pfis 159 to 150 ma raw data from sfis degassed during the initial crushing steps form scatters on inverse isochron plots however 2d and 3d k cl ar diagrams yield sfi ages that agree with 40ar 39ar ages of k feldspar veins cutting the tungsten ore bodies

lead in the getchell turquoise ridge carlin type gold deposits from the perspective of potential igneous and sedimentary rock sources in northern nevada implications for fluid and metal sources lead isotope compositions of bulk mineral samples fluorite orpiment and realgar determined using conventional techniques and of ore stage arsenian pyrite using the sensitive high resolution ion microprobe shrimp in the getchell and turquoise ridge carlin type gold deposits osgood mountains require contribution from two different pb sources one pb source dominates the ore stage it has a limited pb isotope range characterized by 208pb 206pb values of 2 000 to 2 005 and 207pb 206pb valuesof 0 8031 to 0 8075 as recorded by 10 mm diameter spot shrimp analyses of ore stage arsenian pyrite these values approximately correspond to 206pb 204pb of 19 3 to 19 6 207pb 204pb of 15 65 to 15 75 and 208pb 204pb of 39 2 to 39 5 this pb source is isotopically similar to that in average neoproterozoic and cambrian clastic rocks but not to any potential magmatic sources whether those clastic rocks provided pb to the ore fluid cannot be unequivocally proven because their pb isotope compositions over the same range as in ore stage arsenian pyrite are similar to those of ordovician to devonian siliciclastic and calcareous rocks the pb source in the calcareous rocks most likely is largely detrital minerals since that detritus was derived from the same sources as the detritus in the neoproterozoic and cambrian clastic rocks the second pb source is characterized by a large range of 206pb 204pb values 18 34 with a limited range of 208pb 204pb values 38 1 39 5 indicating low but variable th u and high and variable u pb values the second pb source dominates late and postore stage minerals but is also found in preore sulfide minerals these pb isotope characteristics typify ordovician to devonian siliciclastic and calcareous rocks around the carlin trend in northeast nevada petrologically similar rocks host the getchell and turquoise ridge deposits lead from the second source was either contributed from the host sedimentary rock sequences or brought into the hydrothermal system by oxidized ground water as the system collapsed late ore and postore stage sulfide minerals pyrite orpiment and stibnite from the betze post and meikle deposits in the carlin trend and from the jerritt canyon mining district have pb isotope characteristics similar to those determined in getchell and turquoise ridge this observation suggests that the pb isotope compositions of their ore fluids may be similar to those at getchell and turquoise ridge two models can explain the pb isotope compositions of the ore stage arsenian pyrite versus the late ore or postore sulfide minerals in either model pb from the ordovician to devonian siliciclastic and calcareous rock source enters the hydrothermal system late in the ore stage but not to any extent during the main stage of ore deposition in one model ore stage pb was derived from a source with pb isotope compositions similar to those of the neoproterozoic and cambrian clastic sequence transported as part of the ore fluid and then deposited in the ore stage arsenian pyrite and fluorite the second model is based on the observation that the pb isotope characteristics of the ore stage minerals also are found in some ordovician to devonian calcareous and siliciclastic rocks hence ore stage pb could have been derived locally and simply concentrated during the ore stage critical to the second model is the removal of all high 206pb 204pb 20 material during alteration it also requires the retention of only the low 206pb 204pb component of the ordovician to devonian sedimentary rocks this critical step is possible only if the high 206pb 204pb values are contained in readily dissolvable mineral phases whereas the low 206pb 204pb values are found only in refractory minerals that released pb during a final alteration stage just prior deposition of auriferous arsenian pyrite distinguishing between pb transported with the ore fluid or inherited from the site of mineral deposition is not straightforward however it is simpler to explain the pb isotope compositions of ore stage arsenian pyrite and fluorite in two different but spatially related carlin type deposits getchell and turquoise ridge with different host rocks by input of pb with the ore fluid once the limited pb in the hydrothermal fluid was exhausted by incorporation in ore stage arsenian pyrite or other ore stage minerals pb from the second source the ordovician to devonian sedimentary rock sequences became available for incorporation in some but not all of the late stage sulfide minerals

direct dating of tin tungsten mineralization of the piaotang tungsten deposit south china by 40ar 39ar progressive crushing abstract dating ore minerals is the most direct method to determine the mineralization age of a deposit but only a few ore minerals can be directly dated by traditional isotopic geochronometers the aim of this study is to investigate the possibility of direct dating of the ore minerals cassiterite and wolframite from the piaotang tungsten deposit using the 40ar 39ar stepwise crushing technique comparing the age to coexisting k rich muscovite dated by 40ar 39ar laser stepwise heating the cassiterite wolframite and muscovite samples were separated from four pieces of ore hand specimens the 40ar 39ar isochron ages of cassiterite and wolframite are concordant with ages of their coexisting muscovite indicating that cassiterite and wolframite are suitable ore minerals for directly dating the ore forming event by 40ar 39ar stepwise crushing

hydrothermal apatite sims th pb dating constraints on the timing of low temperature hydrothermal au deposits in nibao sw china abstract precise geochronology is a crucial tool for understanding the genesis of low temperature hydrothermal mineral deposits but datable minerals are not always available e g mineralization within sedimentary rocks such as carlin type or carlin like au deposits here we demonstrate that hydrothermal apatite associated with au from the large nibao deposit in the yunnan guizhou guangxi region of south china can be dated to yield the age of au mineralization nibao is a carlin like deposit hosted in a permian carbonate bearing pyroclastic breccia the auriferous minerals are predominantly zoned pyrite containing as cu and au rich rims euhedral and subhedral apatite forms a mosaic texture and is intergrown with hydrothermal quartz sericite and zoned auriferous pyrite indicating that the apatite is of hydrothermal origin and was coeval with au mineralization unlike sedimentary and igneous apatite hydrothermal apatite is relatively depleted in lrees enriched in mrees and slightly depleted in eu hydrothermal apatite also has high th u ratios negligible u concentrations and very low concentrations of common pb this makes the apatite a potential candidate for th pb dating our sims th pb analyses yield a weighted mean 232th 208pb age of 141 3 ma n 23 mswd 2 2 for apatite coeval with auriferous pyrite and this is the best estimate of the timing of au mineralization hydrothermal apatite is also present in similar deposits in the golden triangle of south china therefore th pb dating of hydrothermal apatite potentially allows for the accurate dating of low temperature hydrothermal deposits in china and worldwide

calcite sm nd isochron age of 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 it is hosted in permian bioclastic limestone near the axis of an anticline hydrothermal calcite is common on the periphery of central zones of ferroan carbonate dissolution that provided the main source of iron that was sulfidized during gold deposition these calcite veins contain relatively high concentrations of rare earth elements with mree enriched patterns and yield sm nd isochron ages of 134 3 ma to 136 3 ma with significant different initial end values of 12 9 and 2 0 respectively these ages are interpreted to record age of decarbonation and gold deposition during the late stages of yanshanian orogeny the initial nd isotopic compositions of the calcites suggest that nd was primarily derived from the permian longtang formation that hosts all ore bodies at the deposit this study shows that sm nd isotopic compositions of hydrothermal calcites can be used to constrain the age and source of nd in carlin type gold deposits

low temperature thermochronology of the carlin type gold deposits in southwestern guizhou china implications for mineralization age and geological thermal events abstract the dian qian gui area in southwestern china is the second largest concentration of the carlin type gold deposits in the world and the southwestern guizhou is the most important gold producing district of the dian qian gui area dating of the carlin type gold deposits is always a challenge due to the lack of ore stage minerals which are suitable for conventional radiometric dating low temperature thermochronometers including fission track and u th he are temperature sensitive radiometric dating techniques and have been successfully applied to elucidate many aspects of ore deposits including the timing and duration of mineralization processes in this study zircon fission track zircon u th he and apatite fission track dating techniques were applied to the carlin type gold deposits in southwestern guizhou samples for zircon and apatite analyses were collected from mineralized or altered sedimentary rocks in shuiyindong taipingdong bojitian yata and getang gold deposits four groups of thermochronological ages were obtained i e 192 216 ma 132 160 ma 88 ma and 19 40 ma which are considered to be the records of four geological thermal events of them most zircon fission track ages and all zircon u th he ages concentrate in 132 160 ma thermochronological constraints combined with field relationships suggest that the mineralization of the carlin type gold deposits in southwestern guizhou most likely occurred in this period partial zircon fission track ages are in 192 216 ma they may record the cooling timing of a pre ore thermal event caused by the indosinian orogeny which is supported by the paleogeotemperature restoration a few zircon grains with high u content yield fission track age of 88 ma which may record a post ore thermal event associated with the intrusion of local mafic dykes all apatite fission track ages range in 19 40 ma which may record a lower temperature but extensive hydrothermal superimposition in the cenozoic additionally a corresponding relationship between zircon fission track ages and stratigraphic sequences was identified in the huijiabao anticline which is considered to reflect the decrease of temperature and duration of ore forming hydrothermal activity from lower to upper stratigraphic sequences

part 1 regional studies and epithermal deposits northern nevada is one of the earth s premier gold and silver producing regions and gold and silver are mined from a wide range of deposit types table 1 current production largely comes from carlin type sedimentary rock hosted disseminated gold deposits christensen 1995 teal and jackson 1997 bettles 2002 many of which lie along linear trends fig 1 roberts 1960 1966 berger and bagby 1991 the small area of the carlin trend approximately 8 x 65 km is north america s most prolific gold mining district producing nearly 125 t 4 moz of gold annually since large scale mining began in 1965 with the opening of the carlin mine the carlin trend has produced more than 1555 t 50 moz of gold during 2001 gold production from the entire state of nevada was nearly 253 t 8 13 moz which accounted for approximately 76 percent of the united states and 10 percent of the world production price and meeuwig 2002 in 2001 only the countries of south africa and australia produced more gold than the state of nevada in addition nevada produced 543 t 17 4 moz of silver in 2001 about 31 percent of the united states production and 3 percent of the world production in 1996 the mineral resources program of the u s geological survey began a multidisciplinary project to investigate the origin of gold deposits in northern nevada this project was undertaken in collaboration with the nevada bureau of mines and geology the ralph j roberts center for research in economic geology at the university of nevada reno several other universities and numerous mining companies active in the region in addition several universities and mining companies were conducting research on the origin of gold deposits in northern nevada this research built on more than a century of studies by the

dating gold deposition in a carlin type gold deposit using rb sr methods on the mineral galkhaite significant effort has been expended in an attempt to date hydrothermal activity that generated carlin type gold deposits ctds in the great basin of nevada thus far these efforts have been only partially successful because the relationship s between the dated mineral and hydrothermal activity are equivocal in many cases galkhaite a trace component of at least four ctds in nevada contains significant amounts of rb and virtually no sr making it an ideal candidate for radiometric dating at the getchell deposit galkhaite is paragenetically late but clearly associated with gold mineralization our data place gold mineralization at getchell at 39 0 2 1 ma this is the first unequivocally gold related date produced for any of the carlin type systems galkhaite also has been reported at the carlin rodeo and betze deposits and is likely present in other ctds in nevada this mineral may provide a solution to the conundrum of dating of ctds

the tuscarora au ag district eocene volcanic hosted epithermal deposits in the carlin gold region nevada the tuscarora mining district contains the oldest and the only productive eocene epithermal deposits in nevada the district is a particularly clear example of association of low sulfidation deposits with igneous activity and structure and it is unusual in that it consists of two adjoining but physically and chemically distinct types of low sulfidation deposits moreover tuscarora deposits are of interest because they formed contemporaneously with nearby giant carlin type gold deposits the tuscarora deposits formed within the 39 9 to 39 3 ma tuscarora volcanic field along and just outside the southeastern margin of the caldera like mount blitzen volcanic center both deposit types formed at 39 3 ma contemporaneous with the only major intrusive activity in the volcanic field no deposits are known to have formed during any of the intense volcanic phases of the field intrusions were the apparent heat source and structures related to the mount blitzen center were conduits for hydrothermal circulation the ore forming fluids interacted dominantly with eocene igneous rocks the two deposit types occur in a northern silver rich zone that is characterized by relatively high ag au ratios 110 150 narrow alteration zones and quartz and carbonate veins developed mostly in intrusive dacite and in a southern gold rich zone that is typified by relatively low ag au ratios 4 14 more widespread alteration and quartz fissure and stockwork veins commonly developed in tuffaceous sedimentary rocks the deposit types have similar fluid inclusion and pb and s isotope characteristics but different geochemical signatures quartz veins from both zones have similar thermal and paragenetic histories and contain fluid inclusions that indicate that fluids cooled from between 260 and 230 c to less than 200 c fluid boiling may have contributed to precious metal deposition veins in both zones have relatively high as and sb and low bi te and w the silver zone has high ca pb mn zn cd tl and se the gold zone has high hg and mo a few samples from an area of overlap between the two zones share chemical characteristics of both deposit types the deposit types could represent a single zoned or evolving system in which hydrothermal fluids rose along structures within the silver zone preferentially deposited ag and base metals and then spread into the gold zone alternatively the deposit types could represent two distinct but temporally indistinguishable hydrothermal cells that only narrowly overlapped spatially as noted in previous studies the hydrothermal fluids that generated the tuscarora and other epithermal deposits could have evolved from carlin type fluids by boiling and mixing with meteoric water if so the tuscarora deposit may represent epithermal conditions above carlin type deposits and carlin type deposits may lie beneath the district

numerical modeling of the late weichselian svalbard barents sea ice sheet abstract previous reconstructions of the ice cover of the svalbard barents sea region during the late weichselian have ranged from small ice masses on svalbard to complete inundation of the barents shelf region by an ice sheet several kilometers thick we have used a time dependent finite difference numerical model to undertake a new glaciological reconstruction for the svalbard barents sea ice sheet over the last 30 000 yr the numerical model requires environmental forcing functions in the form of air temperature and precipitation and their behavior with respect to altitude together with sea level change and an iceberg calving relation ice buildup on svalbard is calculated to have begun 28 000 yr ago and maximum dimensions were reached by 20 000 yr ago covering svalbard and the northwestern barents sea with a center of mass 1 3 km thick around eastern svalbard decay was complete by about 10 000 yr ago the margin of the modeled ice sheet at its maximum is in good agreement with observed sea floor morphological features but there are discrepancies in timing between the modeled ice sheet decay and i a dated meltwater spike in fram strait and ii the observed rebound curves for svalbard an inverse approach was used to predict ice sheet decay and it was found that increasing the rate of iceberg calving within the model produces a deglaciation some 2000 yr earlier which is compatible with these two independent datasets the reconstruction is also compatible with geological evidence on the isostatic response of bjornoya close to the southern limit of the ice sheet and seismically observed deposits interpreted to be ice proximal facies located in the northwestern barents sea our time dependent model reconstructions of the svalbard barents sea ice sheet indicate ice cover over only the northwestern barents sea during the late weichselian but this does not preclude the presence of ice derived from fennoscandia and the kara sea region elsewhere in the barents sea

data for distinguishing generations of quartz and a distinct gas signature of deep high grade carlin type gold mineralization using quadrupole mass spectrometry abstract carlin type gold deposits in north central nevada occur in a region that was the locus of igneous and or hydrothermal activity over time and the overprinting of silicification associated with metamorphism base metal mineralization barren jasperoid and post ore alteration hinders exploration efforts therefore the potential to distinguish unrelated generations of quartz using the results of quadrupole mass spectrometer qms gas analyses was evaluated for the getchell trend and compared to results from the goldstrike property in the carlin trend and a carlin type gold occurrence in the huijiabao trend china the results of fluid inclusion petrography qms analyses and interpretation of gas data using n 2 ar he ternary diagrams and co 2 ch 4 vs n 2 ar plots indicate that different generations of quartz in the getchell trend were deposited by hydrothermal fluids having distinct characteristics metamorphic quartz containing one phase ch 4 and halite bearing liquid water dominant vapor poor inclusions has the highest gas content 37 6 mol and highest n 2 ar values 3250 which are suggestive of an evolved magmatic fluid pre ore and quartz base metal veins contain co 2 bearing inclusions base metal veins have n 2 ar values 675 and a positive correlation between h 2 s ar vs n 2 ar that is suggestive of a magmatic fluid carlin type quartz contains liquid dominant vapor poor inclusions and is characterized by total gas contents 10 mol and n 2 ar values 300 that are suggestive of mixed crustal meteoric magmatic fluid sources post ore quartz and barren jasperoid formed from mixtures of gas poor meteoric water and crustal fluids samples of deep high grade mineralization from the goldstrike property have total gas contents up to 10 5 mol and n 2 ar values 300 fluid sources include crustal meteoric and magmatic gas data from the goldstrike property turquoise ridge deposit and metamorphic quartz of the getchell trend plot near the n 2 apex of n 2 ar he diagrams which is indicative of a magmatic fluid end member carlin type mineralization in the huijiabao trend is unique because fluids were ch 4 rich and there is a correlation between ch 4 and hydrocarbons gas analyses commonly record 2 is the dominant gas specie together the results show that fluid inclusion gases can be used to distinguish different generations of quartz in mining districts with complex origins

geology and geochemistry of three sedimentary rock hosted disseminated gold deposits in guizhou province people s republic of china abstract five sedimentary rock hosted disseminated gold deposits have been discovered since 1980 in southwestern guizhou province prc submicron sized gold is disseminated in silty carbonate and carbonaceous shale host rocks of permian and triassic age arsenic antimony mercury and thallium accompany the gold associated hydrothermal alteration resulted in decarbonatization of limestone silicification and argillization and depletion of base metals barium and many other elements organic material occurs in most host rocks and ores it was apparently devolatilized during a regional heating event that preceded hydrothermal activity and thus was not mobilized during mineralization and did not affect gold deposition the geologic setting of the guizhou deposits includes many features that are similar to those of sedimentary rock hosted deposits of the great basin western united states the heavy element suite that accompanies gold is the same but base metals are even scarcer in the guizhou deposits than they are in u s deposits the guizhou deposits discovered to date are smaller than most u s deposits and have no known spatially associated igneous rocks

40 ar 39 ar k ar and fission track geochronology of sediment hosted disseminated gold deposits at post betze carlin trend northeastern nevada the post betze deposit of nevada is the largest sediment hosted disseminated gold deposit presently known both dimensionally and in terms of contained metal ore occurs primarily as submicron sized gold that is disseminated in altered sedimentary rocks of the lower paleozoic roberts mountains formation however significant portions of the ore are present in altered monzonite of the goldstrike stock alteration and mineralization were controlled by both structure and stratigraphy alteration began with early decarbonatization and was followed by silicification and finally argillization phyllosilicate mineral zoning grades from proximal kaolinitc to kaolinitc sericite to unaltered rock based on geochronologic studies utilizing the k ar 40 ar 39 ar and fission track techniques we suggest that the age of gold mineralization is approximately 117 ma the premineralization goldstrike stock was emplaced at about 158 ma and a postmineralization sill was emplaced at 39 ma these events place clear limits on the age of mineralization fine grained sericite that is interpreted to have formed during hydrothermal events which also generated gold ore was dated by either the k ar method or a modification of the standard 40 ar 39 ar fusion technique age determinations on several samples of fine grained sericite from altered host rocks both sedimentary and igneous yield ages near 117 ma younger dates are interpreted to be the result of either thermal disturbance of the k ar system or mixing of sericites of two ages one sample of coarser grained sericite that was stepheated gave discordant spectra fission track analyses of zircon and apatite from the postore sill clearly document the lack of significant thermal or hydrothermal activity younger than 39 ma although less definitive fission track data on zircon from preore sedimentary and igneous hosts suggest that no widespread hydrothermal activity having temperatures above about 100 degrees c has occurred since approximately 110 ma the 117 ma age is consistent with one of the major magmatic pulses recognized in the northern great basin it is also similar to within analytic uncertainty a k ar date of 109 ma from the welches canyon stock 20 km south of post betze an intrusion of similar age unexposed at present could have been the driving force for the hydrothermal system at post betze published geochronologic data though less well tied to mineralization suggest similar mid cretaceous ages for other sediment hosted disseminated gold deposits in nevada based on these ages we suggest that sediment hosted disseminated gold deposits are not necessarily products of extensional environments and in fact appear to be associated with compressional environments in nevada during cretaceous time the alignment of sediment hosted disseminated gold deposits and other features in the basin and range province of the western united states suggests that zones of long term crustal weakness may have controlled igneous intrusion and consequent hydrothermal gold mineralization although not all igneous episodes necessarily generated sediment hosted disseminated gold ore deposits the strong association between sediment hosted disseminated gold deposits the precambrian craton and these deep seated structures also suggests the possibility of a deep source for gold and other components of these systems

timing of gold and arsenic sulfide mineral deposition at the getchell carlin type gold deposit north central nevada pregold mineralization at the getchell carlin type gold deposit includes quartz and base metal vein mineralization associated with intrusion of a cretaceous granodiorite stock the veins contain minor pyrite and trace chalcopyrite arsenopyrite galena and sphalerite the pyrite is moderately coarse and in thin section has high relief is well polished and is fractured and locally cemented by the gold ore assemblage white micas are associated with veins near the granodiorite intrusion gold was not observed or detected by fire assay analyses of samples or electron microprobe analyses of pyrites microprobe analyses show that pregold pyrites have near stoichiometric compositions variable low arsenic is present in pyrite in samples overprinted by gold mineralization secondary ion mass spectrometry sims analyses detected trace gold in the coarse near stoichiometric pyrite in overprinted samples the pregold vein assemblage was fractured and cemented by gold ore stage mineralization the gold ore stage assemblage consists of gold and arsenic enriched pyrite and marcasite encompassed by jasperoid and drusy quartz and local late fluorite orpiment and galkhaite the consistent spatial association of jasperoid and ore pyrite reflects their near contemporaneous formation the ore pyrite occurs as either fine irregularly shaped grains or rims on earlier gold free pyrite in thin section the pyrite is visibly distinct and has a low polishing relief and a poor polish sims and electron microprobe analyses show that ore pyrites commonly contain 8 to 11 wt percent arsenic and as much as 2 400 ppm gold near the end of the ore stage fluorite orpiment and galkhaite precipitated locally in open space created by faulting or limestone dissolution late ore stage mineralization consists dominantly of open space filling realgar and calcite with minor quartz stibnite and framboidal pyrite realgar conforms to euhedral crystal faces of ore stage quartz fluorite and galkhaite calcite filled most remaining open space and conforms to euhedral crystal faces of quartz fluorite and realgar significant textural observations argue against an earlier interpretation that the gold mineralization and arsenic minerals formed as two discrete events separated by 40 m y in a few areas where calcite and realgar are in contact with ore stage quartz containing gold bearing pyrite realgar and calcite enclose gold bearing pyrite grains massive realgar and calcite distal from these contacts do not contain the gold bearing pyrite the presence of ore pyrite in realgar calcite and jasperoid requires close timing of these minerals and shows that there is no major time break separating ore stage and late ore stage mineral deposition textures indicate instead that the ore stage and late ore stage formed as part of a single evolving hydrothermal system the consistent successive overgrowth of younger minerals on perfectly preserved euhedral faces of older minerals supports the continuous evolution of the gold ore stage into the late ore stage these results are consistent with fluid inclusions that indicate that paragenetically successive minerals precipitated from an aqueous ore fluid with consistent salinity and gas contents but at declining temperatures results show that within error the 34 39 and 42 ma ages determined for fluorite and galkhaite at getchell and adularia at the nearby twin creeks mine respectively most closely approximate the timing of gold deposition at getchell

evaluation of radioisotope dating of carlin type deposits in the great basin western north america and implications for deposit genesis a variety of techniques have been used in attempts to date the mineralization in carlin type deposits in the great basin with highly variable results these techniques and results are reviewed in this paper along with presentation of two new dates for the rodeo deposit on the carlin trend and for the barneys canyon deposit in utah complete resetting of sericite by hydrothermal fluids of the temperature and duration of hydrothermal activity that form carlin type deposits is considered highly unlikely therefore dates from sericite are generally of questionable value unless that sericite can be shown to have formed during the same hydrothermal event during which au was deposited for the deposits that have been investigated to date sericite dates rarely if ever record the age of au mineralization however sericite ages do appear to record pre au events in some districts such events may have contributed to ground preparation and to a much lesser extent to the tenor of the ore fission track and u th he techniques provide important age constraints on mineralization in some districts but also suffer from a less than clear association with au rb sr dating of galkhaite an hg sulfosalt provides the only direct age of mineralization but galkhaite has been recognized in only a few locations and dated in only two deposits in a similar manner adularia is contemporaneous with au at twin creeks but twin creeks is the only carlin type deposit where adularia has been reported several other techniques u pb reos sm nd have been used in attempts to date the deposits but with limited success the best available ages are those from preore and postore igneous events and those from galkhaite galkhaite from getchell indicates a mineralization age of 39 ma and that from rodeo carlin trend indicates a mineralization age of 40 ma a new u th he age 34 ma for apatite at barneys canyon suggests contemporaneity with the nearby bingham porphyry cu system the most reliable data from several deposits and districts in the great basin indicate that carlin type mineralization occurred in a relatively narrow time interval between 33 and 42 ma this interval coincides with the transition from a compressional to an extensional tectonic environment in the region although similar tectonic environments have existed at different times and places in western north america no other carlin type mineralization is known to exist in the region therefore although the age and tectonic environment of these deposits is now reasonably well constrained it is clear that tectonic environment alone is insufficient to explain the genesis of carlin type deposits additional perhaps unique factors such as host rock geochemistry must have contributed to the development of these exceptional deposits

ore fluid properties and sources from quartz associated gold at the betze post carlin type gold deposit nevada united states quartz at the betze post deposit the largest carlin type gold system in the world was examined to better understand ore fluid properties and sources that generated carlin type gold deposits detailed petrography and paragenesis investigations distinguished textural relationships luminescence various generations of quartz and fluid inclusion populations microthermometry chemical analyses of quartz and in situ and conventional oxygen isotope analyses of quartz provided information about hydrothermal fluid conditions as well as fluid sources and ore formation processes pre syn late and post ore stages of quartz were distinguished during petrographic studies and confirmed by cathodoluminescence analyses ore stage jasperoid and late ore drusy quartz are spatially associated with au bearing pyrite both lack luminescence two generations of post ore drusy quartz overgrew ore and late ore quartz and exhibit bright and multiply zoned luminescence electron probe microanalyses determined that nonluminescing ore and late ore quartz have elevated concentrations of al in contrast to post ore luminescent quartz that contains low trace element concentrations fluid inclusion microthermometry determined that ore stage fluids had low salinities generally 5 wt nacl equiv and were trapped at 180 to 240 c the 18o values calculated for inclusion fluids and determined for quartz using in situ ion probe and conventional analyses indicate that the isotopic composition of hydrothermal fluids became 18o depleted with time from the ore stage through the late ore stage to the post ore stage the 18o composition of each stage of quartz also varies spatially across the betze post deposit and 18ovsmow values of ore late ore and post ore stage quartz became more depleted with increasing distance from the master post fault these patterns are interpreted to result from increasing dilution of the 18o enriched ore fluid by unevolved meteoric fluids over time and with increased ore fluid transport distance to the west away from the post fault the master fault that transmitted hydrothermal fluids to the deposit oxygen isotope results are consistent with a low fluid rock ratio during upward transport of the ore fluid via the post fault below the deposit some ore fluids were diverted into the jb series faults associated with the betze ore zones and the shalosky fault associated with the screamer ore zone in the western part of the deposit ore fluids were increasingly diluted by meteoric fluids with distance as ore fluids traveled away from the post fault and over time as different stages of quartz precipitated acidic 180 to 240 c ore fluids accessed the level of the deposits where they reacted with the devonian popovich formation and precipitated nonluminescing al enriched ore stage jasperoid and late ore drusy quartz along with au and trace element rich pyrite fluid rock reaction dissolution and replacement of silty carbonate host rocks may have produced al that substituted for si in non luminescing jasperoid and late ore stage quartz as the hydrothermal ore system began to cool and collapse late ore drusy quartz and realgar precipitated in open space as ore stage pyrite precipitation declined the hydrothermal system collapsed with meteoric water flooding post ore minerals including luminescent al poor post ore drusy quartz and later calcite and barite precipitated either from latest carlin related fluids neutralized by infiltration of meteoric waters or as part of a later separate hydrothermal event

re os isochron ages for arsenopyrite from carlin like gold deposits in the yunnan guizhou guangxi golden triangle southwestern china abstract the yunnan guizhou guangxi golden triangle is considered to be one of the regions hosting carlin like gold deposits in china gold deposits in this region can be grouped into lode type that are controlled by faults and layer like type controlled by stratigraphy arsenopyrite is one of the major gold bearing minerals in these deposits rhenium os isotopic dating of arsenopyrite from the lode type lannigou and jinya and the layer like type shuiyindong gold deposits yields isochron ages of 204 19 ma 206 22 ma and 235 33 ma respectively the data suggest that the carlin like gold deposits formed in late triassic to early jurassic which is clearly earlier than the ca 100 80 ma acid to ultra basic magmatism in this part of southwestern china the ages are consistent with ore formation during a period of post collisional lateral transpression which is similar to that of the carlin like gold deposits in western qinling of china but quite different from carlin type gold deposits in nevada u s a

in situ sims u pb dating of hydrothermal rutile reliable age for the zhesang carlin type gold deposit in the golden triangle region sw china the contiguous region between guangxi guizhou and yunnan commonly referred to as the golden triangle region in sw china hosts many carlin type gold deposits previously the ages of the gold mineralization in this region have not been well constrained due to the lack of suitable minerals for radiometric dating this paper reports the first sims u pb age of hydrothermal rutile crystals for the zhesang carlin type gold deposit in the region the hydrothermal u bearing rutile associated with gold bearing sulfides in the deposit yields an u pb age of 213 6 5 4 ma which is within the range of the previously reported arsenopyrite re os isochron ages 204 19 to 235 33 ma for three other carlin type gold deposits in the region our new and more precise rutile u pb age confirms that the gold mineralization was contemporaneous with the triassic w sn mineralization and associated granitic magmatism in the surrounding regions based on the temporal correlation we postulate that coeval granitic plutons may be present at greater depths in the golden triangle region and that the formation of the carlin type gold deposits is probably linked to the coeval granitic magmatism in the region this study clearly demonstrates that in situ rutile u pb dating is a robust tool for the geochronogical study of hydrothermal deposits that contain hydrothermal rutile

40 ar 39 ar dating and mineral paragenesis for carlin type gold deposits along the getchell trend nevada evidence for cretaceous and tertiary gold mineralization the orebodies at the getchell and twin creeks mines were studied through mineral paragenesis geologic relationships and 40 ar 39 ar dating mineral paragenetic relationships are based on observations made during the logging of 18 000 m of drill cuttings and core and crosscutting relationships recognized in the field and main pit at the getchell mine ages for igneous and mineralizing events were determined through 40 ar 39 ar incremental heating analyses of 15 samples of biotite k feldspar sericite and vein adularia a thermal history for the area was also developed using k feldspar multiple diffusion domain results and age determinations on cogenetic minerals which have different argon closure temperatures mineral paragenetic relationships and 40 ar 39 ar dating at the getchell and twin creeks deposits document that gold mineralization occurred in five stages between 95 and 42 ma stage 1 pyrrhotite quartz arsenopyrite chalcopyrite biotite gold mineralization in skarn is associated with 95 ma dacite dikes and granodiorite plugs stage 2 chalcopyrite sphalerite galena pyrite arsenopyrite or gold and silver mineralization in skarn is related to the 92 ma osgood mountains stock secondary k feldspar and sericite in stage 3 quartz pyrite kaolinite gold mineralization formed at 83 ma and are not related to 95 or 92 ma igneous activity stage 4 low grade quartz pyrite gold mineralization formed at about 75 ma in the matrix of a breccia pipe that cuts 83 ma silicic and argillic ores adularia intergrown with stibnite orpiment pyrite quartz gold or realgar mineralization yields precise 40 ar 39 ar plateau ages of 42 11 or 0 43 and 41 90 or 0 25 ma for stage 5 this study documents the temporal complexity of mineralization and igneous activity at the getchell and twin creeks deposits minor gold in skarn type mineralization stages 1 and 2 associated with 95 and 92 ma igneous intrusions preceded and was not genetically related to carlin type gold mineralization stages 3 and 5 the carlin type deposits at getchell and twin creeks therefore represent a composite orebody formed by the overprinting of 83 ma stage 3 quartz pyrite gold by 42 ma stage 5 orpiment stibnite pyrite gold mineralization

fluid mixing during late stage carlin type mineralization in the getchell and twin creeks deposits nevada abstract a stable isotope study of orpiment realgar calcite stibnite mineralization in the getchell and twin creeks deposits nevada was undertaken to determine the origin s of late stage fluids samples of orpiment have d values of 48 4 to 90 5 and 34s values of 0 3 2 2 which are indicative of a magmatic source whereas samples of realgar have d values of 129 1 to 139 7 that are indicative of meteoric water and 34s values of 4 2 4 9 similar to pre ore diagenetic pyrite the d and 13c data of calcite plot to form a mixing trend between fluids with magmatic and meteoric sources fluid mixing and wall rock interaction is supported by the distribution of data in a d and 18oh2o plot for calcite additional evidence of fluid mixing is provided by d values of 55 4 to 137 9 for stibnite these data document how a magmatic fluid produced orpiment au mineralization fluid mixing occurred during calcite deposition and barren realgar formed from a meteoric water