the impact of hydrothermal mineral replacement reactions on the formation and alteration of carbonate hosted polymetallic sulfide deposits a case study of the artemis prospect queensland australia abstract hydrothermal sulfidation of carbonate rocks and the reverse replacement of sulfides by carbonates are important processes responsible for the formation and subsequent alteration of ore deposits these processes have been recognized in the case study of the artemis zn cu au prospect which is located in the cloncurry district within the eastern succession of the mount isa inlier nw queensland australia the high grade polymetallic mineralization displays a complex association of massive sulfides and carbonates hosted in a vertical marble lens adjacent to garnet bearing schist staurolite muscovite schist and quartzo feldspathic psammite petrographic analyses of drill core specimen by optical and electron microscopy micro x ray florescence elemental maps electron probe microanalyses cathodoluminescence and bulk geochemistry suggested three major stages of mineralization i pre ore stage marble calcite 0 ii ore stage involving sulfidation of the marble and precipitation of calcite 1 and spherical sulfide inclusions in the first episode and the formation of calcite 2 and massive sulfide in the second episode and iii post ore stage involving replacement of sulfides by calcite 3 and garnet mineral replacement reactions are dominant processes in rocks of ore stage and post ore stage the ore stage involved the dissolution of coarse and pristine calcite 0 ca0 95mn0 3fe0 2co3 and the precipitation of sulfides and calcite 1 ca0 96mn0 3fe0 1co3 and calcite 2 ca0 96mn0 3fe0 1co3 the sulfide assemblage consists of pyrrhotite sphalerite chalcopyrite galena arsenopyrite cobaltite costibite bi cubanite ag sulfides and au in decreasing order of abundance in episode 1 calcite 1 contains spherical sulfide inclusions while in episode 2 calcite 2 envelopes calcite 1 the replacement of co rich arsenopyrite fe0 75co0 26as1 13s0 83 by relatively co poor arsenopyrite fe0 86co0 15as0 99s0 99 via a coupled dissolution precipitation reaction occurred in episode 2 based on arsenopyrite geothermometry the temperatures for the first and second episode are 650 50 and 450 70 c respectively micro xrf elemental maps of the garnet bearing schist adjacent to the sulfidized marble revealed the sulfidation front where pre ore garnet and amphibole were replaced by pyrrhotite chalcopyrite au biotite and muscovite in the post ore stage calcite 2 was partially replaced by siderite and calcite 3 ca0 94mn0 4fe0 2mg0 1co3 which shows sectoral and oscillatory zoning galena was replaced by calcite 3 as documented by embayed lobate grain boundaries between these minerals and pyrrhotite fe 1 x s x 0 091 0 119 was pervasively replaced by garnet mn1 2fe1 2ca0 6 al2si3o12 the microscale investigations of the mineralization processes in the artemis orebody document the impact of hydrothermal mineral replacement reactions on metal sequestration mineral replacement reactions facilitate the formation of ore deposits and subsequent alteration processes which may lead to the loss of economic value of the deposit

mineralogy and geochemistry of gold bearing arsenian pyrite from the shuiyindong carlin type gold deposit guizhou china implications for gold depositional processes arsenian pyrite in the shuiyindong carlin type gold deposit in guizhou china is the major host for gold with 300 to 4 000 ppm au and 0 65 to 14 1 wt as electron miroprobe data show a negative correlation of as and s in arsenian pyrite which is consistent with the substitution of as for s in the pyrite structure the relatively homogeneous distribution of gold in arsenian pyrite and a positive correlation of as and au with au as ratios below the solubility limit of gold in arsenian pyrite suggest that invisible gold is likely present as au1 in a structurally bound au complex in arsenian pyrite geochemical modeling using the laser ablation inductively coupled plasma mass spectrometry la icp ms analysis of fluid inclusions for the major ore forming stage shows that the dominant au species were au hs 2 77 and auhs aq 0 23 gold hydroxyl and gold chloride complexes were negligible the ore fluid was undersaturated with respect to native au with a saturation index of 3 8 the predominant as species was h3aso30 aq pyrite in the shuiyindong deposit shows chemical zonation with rims richer in as and au than cores reflecting the chemical evolution of the ore bearing fluids the early ore fluids had relatively high activities of as and au to deposit unzoned and zoned arsenian pyrite that host most gold in the deposit the ore fluids then became depleted in au and as and formed as poor pyrite overgrowth rims on gold bearing arsenian pyrite arsenopyrite overgrowth aggregates on arsenian pyrite indicate a late fluid with relatively high activity of as the lack of evidence of boiling and the low iron content of fluid inclusions in quartz suggest that iron in arsenian pyrite was most likely derived from dissolution of ferroan minerals in the host rocks with sulfidation of the dissolved iron by h2s rich ore fluids being the most important mechanism of gold deposition in the shuiyindong carlin type deposit

relative array analysis of upper mantle lateral velocity variations in southern california spatial averaging of short period teleseismic p wave arrivals across scarlet constrains upper mantle lateral velocity variations beneath southern california we compare dt d back azimuth and averaged arrival time estimates determined from the entire network for 154 events to the same parameters derived from small subsets of scarlet the resulting relative array diagrams and plots of net subarray delays computed for 171 overlapping subarrays exhibit large anomalies that vary smoothly as a function of subarray position implying substantial lateral heterogeneity under the network patterns of mislocation vectors for more than 100 subarrays permit identification of an east west striking high velocity antiform beneath the transverse ranges further constraints on both the lateral configuration and depth of the anomaly are obtained through thin lens analysis of the net delay data where all the time perturbations are assumed to originate at a single depth projection of 2798 net delays requires a lens deeper than 100 km a representative lens at 150 km depth features low velocities beneath the salton trough as well as a concentrated high velocity zone between 116 3 118 3 w and 33 7 34 8 n consistent with the relative array diagrams and the pkp delay contours of hadley and kanamori 1977 therefore the bulk of the high velocity material observed by hadley and kanamori may in fact lie at or deeper than 150 km rather than 40 100 km this possibility prompts renewed speculation regarding the relationship of this body to the plate tectonic history of the region

laser ablation icp ms trace element systematics of hydrothermal pyrite in gold deposits of the kalgoorlie district western australia the kalgoorlie district in the archean yilgarn craton of western australia contains two world class gold deposits the giant golden mile shear zone system and the mt charlotte quartz vein stockworks mineralization occurs in three styles a fimiston style is characterized by ankerite pyrite hematite magnetite gold replacement b oroya style overprints fimiston ore in the shear zones and is characterized by silica ankerite v muscovite pyrite pyrrhotite gold telluride replacement and c mt charlotte style is characterized by veins with ankerite sericite albite pyrite pyrrhotite gold selvages hydrothermal pyrite is ubiquitous in all styles and occurs in several stages laser ablation inductively coupled plasma mass spectrometry la icp ms spot analyses n 652 were collected on 54 representative samples of pyrite from three deposits smooth sections in the ablation spectra were selected for quantitative analysis excluding peaks caused by micron sized inclusions linear mixed effects lme modeling of the analytical results indicates no systematic differences between the fimiston oroya and mt charlotte styles the variance introduced to the dataset by geological variability reflected in random differences between samples and deposits is large this may be a major reason for difficulties in distinguishing the differences due to mineralization style however there are clear differences between pyrites co existing with different mineral assemblages these indicate a strong control on pyrite chemistry by the composition of the hydrothermal fluids finally au te as systematics show that a substantial proportion of the analyzed pyrites in all deposits fall into the field of gold saturation consistent with the known metallurgical character of the ores mineralogical studies ultra fine grinding and recovery by cyanide leach show that 82 of all gold is present in native grains or in au ag tellurides the refractory nature of the fimiston pyrite concentrates is due to clusters of micron to nano sized inclusions rather than due to abundant lattice bound gold

lateral velocity variations in southern california i results for the upper crust from pg waves the plate boundary and major crustal blocks in southern california are imaged by a tomographic backprojection of the pg first arrivals recorded by the southern california array the method formulated specifically for local earthquake arrival times is a fast iterative alternative to direct least squares techniques with it we solve the combined problem of determining refractor velocity perturbations and source and station delays resolution and variance are found empirically by using synthetic examples a map showing lateral velocity variations at a depth of approximately 10 km is presented the results show a strong correlation with surface tectonic features clear velocity contrasts exist across the san andreas the san jacinto and the garlock faults the mojave region has the slowest velocities while the peninsula ranges have the highest the san jacinto block has velocities intermediate between mojave and peninsula range velocities and also has early station delays this may indicate that the san jacinto block has overridden mojave material on a shallow detachment surface no velocity variations are found associated with the transverse ranges which we interpret to mean that the surface batholithic rocks in this area do not extend to pg depths

gold bearing arsenian pyrite and marcasite and arsenopyrite from carlin trend gold deposits and laboratory synthesis invisible gold in natural and synthetic arsenian pyrite and marcasite correlates with anomalous as content and fe deficiency and high contents of invisible gold in most natural and all synthetic arsenopyrite correlate with excess as and fe deficiency as rich fe deficient arsenopyrite synthesized hydrothermally contains up to 3 0 wt au uniformly distributed in growth zones of light backscattered electron contrast at the deep star gold deposit carlin trend nevada the sulfide compositions apparently span the full range of metastability from fesz to near feass 40 at s arsenian pyrite contains up to 0 37 wt au but arsenopyrite has excess s and is relatively au poor observed minimum fe contents are 29 1 at in arsenian pyrite and marcasite from the deep star deposit and 31 3 at in synthetic arsenopyrite we suggest that invisible gold in arsenian pyrite and marcasite and arsenopyrite from sediment hosted gold deposits represents au removed from ore fluids by chemisorption at as rich fe deficient surface sites and incorporated into the solids in metastable solid solution however the oxidation state of invisible gold aua au1 remains uncertain because the chemisorption process is intrinsically nonsystematic in terms of crystal chemical parameters and does not result in definitive atomic substitution trends

geochemistry and textures of gold bearing arsenian pyrite twin creeks nevada implications for deposition of gold in carlin type deposits this study relates morphology size texture and chemistry of arsenian pyrite in the twin creeks carlin type gold deposits to the chemical position and amount of gold that it contains arsenian pyrite is confirmed as the most important gold hosting mineral and four types of gold bearing arsenian pyrite are recognized among these four types the lowest amount of gold and arsenic 1 wt as 17 60 ppm au is contained in arsenian pyrite with relatively large grain sizes 10 30 mu m it formed at relatively high temperatures 250 degrees c and k super h super ratios adularia stable probably relatively slowly the largest amount of gold and arsenic 1 05 2 43 wt as 595 1 465 ppm au is contained in arsenian pyrite with small grain sizes up to 2 mu m that formed at low temperatures 120 degrees 200 degrees c and moderate k super h super ratios illite stable probably by relatively rapid deposition xanes exafs and sims analyses show that gold in arsenian pyrite is both structurally bound au i and in submicroscopic inclusions of free gold au highest amounts of structurally bound gold were observed in the relatively coarse grained arsenian pyrite noted above whereas most inclusions of free gold were observed in fine grained arsenian pyrite in general there is a good correlation between gold and arsenic in arsenian pyrite although au as ratios vary from one pyrite to another it is suggested that gold in arsenian pyrite was deposited by direct deposition of native gold and by adsorption of au i from hydrothermal solutions adsorption of gold by arsenian pyrite can take place from solutions that are not saturated with respect to native gold relative volumes of gold bearing pyrite from different paragenetic stages at twin creeks suggest that as much as 50 percent of the total gold in the deposit could have formed from solutions that were not saturated with respect to native gold because both au and au i are found together in arsenian pyrite it is likely that they were deposited by the same process consideration of possible depositional reactions suggests that a decrease in the activity of reduced sulfur is most likely to cause gold deposition

polarization tomography for p wave velocity structure in southern california we develop a tomographic inversion method that uses teleseismic p wave polarization data to obtain velocity structure polarization inversion has some intrinsic advantages over travel time inversion it is not influenced by source location and origin time errors it is not sensitive to deep mantle velocity structure and can be used iteratively to improve the tomographic result polarization inversion is more sensitive to near station velocity structure and to velocity gradient and is complementary to travel time inversion in this sense the method is applied to california institute of technology u s geological servey southern california array data the result is generally consistent with previous work and also reveals that the high velocity feature beneath the transverse ranges is bounded between 40 and 200 km depths and possibly has a second small piece at about 300 km depth the slow velocity anomaly under the salt on trough is limited to shallow depths less than about 60 km

decoupled geochemical behavior of as and cu in hydrothermal systems cu rich and as rich growth zones in pyrite provide new insights into the composition of late stage magmatic fluids and their host hydrothermal ore deposits the pyrite is from the pueblo viejo dominican republic and yanacocha peru high sulfidation gold silver deposits which are thought to form from hydrothermal systems that interacted with magmatic vapor plumes electron microprobe analysis secondary ion mass spectrometry and elemental maps show that pyrite the most common sulfide mineral in both deposits contains three different types of growth zones 1 as rich zones that are enriched in au ag sb te and pb 2 cu rich zones with significantly lower concentrations of these elements and 3 barren pyrite zones with no other elements these zones are interpreted to result from mixing between the pyrite forming fluid and vapors that invaded the main hydrothermal system episodically comparison to experimental studies of elemental partitioning and analyses of fumaroles and fluid inclusions from magmatic hydrothermal systems suggests that the as rich vapor formed at high and possibly magmatic temperatures whereas the cu rich vapor formed at lower temperatures possibly during migration of the original magmatic vapor the presence of finely spaced multiple growth zones in pyrite suggests that the composition of at least high sulfidation hydrothermal systems can be affected intermittently and repetitively by vapors probably from underlying magmas

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

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 nature and partitioning of invisible gold in the pyrite fluid system the most characteristic feature of hydrothermal deposits of gold is its intimate association with pyrite microscopically visible gold occurs in pyrite ore as metal particles of 0 1 m in size together with so called invisible gold undetectable by conventional microscopic methods the chemical redox and structural state of this invisible gold and the mechanisms of its incorporation into pyrite remain both inconsistent and controversial since the dawn of economic geology to clarify these issues we performed laboratory experiments to simulate interactions of gold bearing sulfur rich hydrothermal fluids with arsenic free pyrite at temperatures from 350 to 450 c and pressures from 400 to 700 bar typical of the formation conditions of many types of gold deposits gold solubility was measured in these fluids as a function of sulfur speciation and acidity gold redox and structural state in pyrite was characterized by high energy resolution fluorescence detected x ray absorption spectroscopy herfd xas together with more traditional analytical techniques such as scanning electron microscopy sem x ray diffraction xrd electron probe micro analysis epma laser ablation inductively coupled plasma mass spectrometry la icpms and inductively coupled plasma atomic emission spectrometry icp aes results show that dissolved au in sulfide sulfate solutions forms complexes with hydrogen sulfide and tri and di sulfur radical ions whose amounts depend mostly on the fluid ph and total sulfur concentration invisible gold in pyrite occurs as au metal submicron to nano sized particles and chemically bound au i in the form of poly sulfide clusters composed on s au s linear units similar to those in aqueous complexes our findings contest the common belief that au i substitutes for fe and or s in the structure of as poor pyrite the partition coefficient of au i between pyrite and the fluid dpy fl is determined to be 0 15 0 07 at 450 c in a wide range of au fluid phase concentrations 10 1000 ppm but much higher dpy fl values between 10 and 50 are found at 350 c these au partitioning trends coupled with the new data on au molecular environment in pyrite suggest a control of au i incorporation in the mineral by a chemisorption step extrapolated to au contents of hydrothermal fluids of the earth s crust which are typically below 1 ppm our dpy fl values reproduce fairly well the natural au tenors in as poor pyrites 0 1 1 ppm au which are 100 1000 times lower than those typically observed in arsenian pyrites and arsenopyrites 10 1000 ppm au at as tenors of 0 01 10 wt our results thus indirectly highlight a key role played by arsenic in gold enrichment in as bearing iron sulfide ore a role that yet remains to be fully understood and quantified

pn travel times in southern california the pn arrivals recorded from the southern california array have been used to demonstrate regional variations in crustal thickness and pn velocity and to investigate the presence of anisotropy in the mantle over 2800 travel times were used in the analysis the classical time term method was extended to allow the moho velocity to vary in a block type structure the statistical f test shows these effects to be significant crustal delays determined depend on both crustal velocities and moho depth the ventura and los angeles basins have sediment delays which indicate sediment thicknesses near 10 kin the moho depth itself varies by 10 km over southern california with a mean of about 29 kin slightly thicker crust is prevalent in the northwestern corner of the array near the southern coast ranges five kilometers of rapid thinning between the coast and the channel islands is shown by a sharp gradient in the delay times normal crustal thicknesses occur over the rest of the array except for the area east of the salton trough where an anomalously thin crust of 22 km exists this area extends from near the plate boundary into arizona while the peninsular ranges and the san bernadino mountains have small roots the san gabriel mountains have none pn velocities range from 7 6 to 8 2 km s within the array high velocities are found in the mojave and offshore regions low velocities are found in the peninsular ranges and the transverse ranges the analysis supports a mean anisotropy of 0 15 km s with the fast direction at n 75 o w this value represents an average of a parameter that varies considerably in the region

visible gold in arsenian pyrite at the shuiyindong carlin type gold deposit guizhou china implications for the environment and processes of ore formation abstract carlin type gold deposits are best known for the scarcity of visible gold in their ores it has long been recognized that the majority of gold is invisible such that it cannot be resolved by conventional microscopy and resides in arsenian pyrite shuiyindong differs in that sub m to m sized native gold is present in arsenian pyrite veinlets and disseminations it is also the largest 55 tonnes and highest grade 7 to 18 ppm stratabound carlin type gold deposit in guizhou china and has produced 5 tonnes of gold from sulfide refractory ores extracted by underground mining methods in this study an electron microprobe analyzer empa was used to map the spatial distribution of invisible gold and sub m to m size visible gold particles in arsenian pyrite in high grade ore samples from the shuiyindong the samples studied are hosted in permian bioclastic ferroan limestone of the longtan formation and exhibit evidence of decarbonation silicification and sulfidation arsenian pyrite with detectable au 400 to 3800 ppm is disseminated in altered limestone and was deposited in two stages separated by an episode of corrosion in a veinlet the results show that there are two populations of native gold in arsenian pyrite one is comprised of sub m size gold particles 0 1 to 0 2 m that are occasionally present in the gold bearing arsenian pyrite disseminated in the host rocks this arsenian pyrite is interpreted to have been formed by sulfidation of ferroan calcite and dolomite another is comprised of coarser 1 to 6 m native gold grains present in the arsenian pyrite veinlet either on the first stage where it has been corroded or on the second stage the lack of fluid inclusion or other evidence of boiling and the low iron content of fluid inclusions in quartz suggest the veinlet formed by sulfidation of another fluid containing fe the fe bearing fluid may be a depleted ore fluid that gained fe by dissolution of ferroan limestone after h 2 s had been consumed the association of the largest visible gold grains with an episode of corrosion suggests that fluids episodically became undersaturated with arsenian pyrite while remaining saturated with gold e g ph decrease or an increase in the oxidation state this may have resulted from incursion of relatively acidic or oxidized fluids that were able to dissolve arsenian pyrite and remain saturated with gold in this case sulfidation of iron from the host rock was the most important depositional mechanism for au bearing arsenian pyrite with or without grains of native gold

coupling between mineral replacement reactions and co precipitation of trace elements an example from the giant olympic dam deposit abstract the mechanisms of scavenging of minor elements in reactive fluid dominated systems control the distribution nature concentration and reactivity of economically valuable or deleterious elements in many environments ranging from hydrothermal ore deposits to sedimentary basins here we show that in a high grade cu u ore from the super giant olympic dam ore deposit remobilized u was scavenged during the fluid driven replacement of chalcopyrite cufes2 by bornite cu5fes4 hydrothermal experiments show that the pseudomorphic replacement of chalcopyrite by bornite proceeded via an interfaced coupled dissolution reprecipitation icdr reaction mechanism with further bornite growing via overgrowth addition of u vi to the experimental fluid resulted in scavenging of u in the form of nano to micro particles of uraninite uraninite precipitation occurred concurrently with replacement resulting in abundant uraninite decorating the initial surface of the parent chalcopyrite grain as well as the coarse porosity that developed within overgrowth bornite our results highlight the importance of disequilibrium or local equilibrium in controlling the endowment of u in complex ores under far from equilibrium fluid dominated conditions e g during seismic or eruptive events fast fluid movements associated with brecciation and or faulting can lead to fast mineral reactions the resulting ultra local conditions e g surface of reacting mineral reaction induced porosity play an important role in controlling the precipitation of minor elements u in this case and interpretation of precipitation mechanisms as reflecting the evolution of bulk fluid may be erroneous

a tomographic image of mantle structure beneath southern california we determined the variations in seismic structure beneath southern california by using a tomographic method of inversion on teleseismic p delays recorded with the southern california array the algorithm employed was a modified form of an algebraic reconstruction technique art used in medical x ray imaging deconvolution with an empirically estimated point spread function was also used to help in focusing the image the inversion reveals two prominent features beneath the region the first is a thin vertical wedge directly beneath the transverse ranges that is 2 3 faster than the surrounding region this feature deepens to the east attaining a maximum depth of about 250 km beneath the san bernardino mountains the second feature is a major zone of low velocity material that is 2 4 slow under the salton trough rift valley extending to a depth of about 125 km two possible explanations for the spatial association of the transverse ranges with the velocity anomaly below are lithospheric subduction or small scale sublithospheric convection in the region of the big bend of the san andreas fault the low velocity anomaly beneath the salton trough is consistent with convective upwelling there

direct analysis of ore precipitating fluids combined ir microscopy and la icp ms study of fluid inclusions in opaque ore minerals laser ablation inductively coupled plasma mass spectrometry la icp ms in combination with near infrared microscopy of fluid inclusions hosted by ore minerals that are opaque to visible light can provide the composition of ore precipitating fluids we applied the two techniques to well constrained fluid inclusion assemblages hosted by pyrite enargite and quartz to trace the source and evolution of the fluids in high sulfidation epithermal veins overprinting a porphyry copper deposit at rosia poieni romania despite some analytical limitations caused by the sulfide host minerals the data demonstrate that fluids trapped in apparently cogenetic quartz and ore minerals are chemically different systematic changes in major and trace element ratios between liquid vapor vapor rich and brine fluid inclusion assemblages in the three minerals record an evolving fluid source at the porphyry to epithermal transition regarding their cs na k ratios most of epithermal quartz hosted fluid inclusion assemblages form a well defined cluster which coincides with the narrow range of the porphyry stage fluids trapped in early quartz of the porphyry stockwork veins their cu na k ratios are 10 to 100 times lower compared to the pyrite hosted inclusions and correspond to the lowest cu na k ratios recorded for the porphyry stage fluids by contrast pyrite hosted vapor rich fluid inclusions have the highest cu na k similar to the highest cu na k ratios measured in the porphyry stage fluid inclusions the results led to the conclusion that the gangue and ore minerals in the high sulfidation epithermal veins at rosia poieni formed by successive pulses of chemically distinct hydrothermal fluids that were successively exsolved from residual melt batches of a progressively crystallizing magma at greater depth these results are consistent with detailed textural observations but petrography alone could not have led to this unambiguous conclusion

a proposed new type of arsenian pyrite composition nanostructure and geological significance this report describes a new form of arsenian pyrite called as3 pyrite in which as substitutes for fe fe as s2 in contrast to the more common form of arsenian pyrite as1 pyrite in which as1 substitutes for s fe as s 2 as3 pyrite has been observed as colloformic overgrowths on as free pyrite in a hydrothermal gold deposit at yanacocha peru xps analyses of the as3 pyrite confirm that as is present largely as as3 empa analyses show that as3 pyrite incorporates up to 3 05 at of as and 0 53 at 0 1 at 0 27 at 0 22 at 0 08 at and 0 04 at of pb au cu zn ni and co respectively incorporation of as3 in the pyrite could be written like as3 y au 1 y 2 fe2 where au and vacancy help to maintain the excess charge hrtem observations reveal a sharp boundary between as free pyrite and the first overgrowth of as3 pyrite 20 40 nm thick and co linear lattice fringes indicating epitaxial growth of as3 pyrite on as free pyrite overgrowths of as3 pyrite onto as free pyrite can be divided into three groups on the basis of crystal size 8 20 nm 100 300 nm and 400 900 nm and the smaller the crystal size the higher the concentration of toxic arsenic and trace metals the yanacocha deposit in which as3 pyrite was found formed under relatively oxidizing conditions in which the dominant form of dissolved as in the stability field of pyrite is as3 in contrast reducing conditions are typical of most environments that host as1 pyrite as3 pyrite will likely be found in other oxidizing hydrothermal and diagenetic environments including high sulfidation epithermal deposits and shallow groundwater systems where probably kinetically controlled formation of nanoscale crystals such as observed here would be a major control on incorporation and release of as3 and toxic heavy metals in oxidizing natural systems

kinematics of present crust and mantle flow in southern california in the southern california region published geologic studies of prehistoric fault offsets yield at least 81 rates of slip covering various periods of time chiefly since the opening of the gulf of california these rates together with the known geometries of active faults are used to constrain a hand fit block model for present horizontal velocity of the crust the assumptions employed are that these rates apply to the present that the blocks are internally rigid down to the greatest depth of earthquakes and that the over all pacific north american plate motion is correctly given by global models the resulting model fits 67 data within their uncertainties 10 more with a small discrepancy 1 mm yr and fails to accommodate only 4 data 2 of which are inconsistent with other data nominal precision is good 3 mm yr but accuracy and uniqueness are both suspect because many block boundaries are questionable despite its many local defects this model suggests four reliable regional conclusions first the rate of shortening on the south side of the transverse ranges varies from 6 to 14 mm yr increasing eastward which implies an unrecognized seismic hazard unless the motion is taken up by folding or fault creep second the pattern of block rotation rates is quite different from the pattern of rotations shown by tertiary paleomagnetic declinations which implies some major pliocene reorganization of blocks third the great bend left step of the plate boundary fault system in the transverse ranges appears to be straightening gradually by a 3 m y clockwise rotation relative to both plates finally if it is assumed that plate shortening has been occurring at this bend since the early pliocene and that crust and upper mantle velocities are similar then this model predicts mantle lithosphere downwelling to at least 250 km depth beneath the transverse ranges this prediction is consistent with upper mantle seismic velocity structure

detecting magmatic derived fluids using pyrite chemistry example of the chibougamau area abitibi subprovince quebec abstract magmatic fluids are an important carrier of precious and base metals in many mineralized systems porphyry deposits intrusion related gold systems irgs volcanogenic massive sulfides vms recognizing magmatic inputs is essential for understanding metallogenic processes and for developing accurate exploration models and the importance of fluids exsolved from magmas remains a source of much debate for some contexts such as irgs and orogenic gold deposits this study aims to identify magmatic fluids in the chibougamau area northeastern corner of the neoarchean abitibi subprovince canada using pyrite chemistry this is achieved by comparing the chemistry of pyrites recovered from the cu au magmatic hydrothermal porphyry systems of the chibougamau area to background compositions i e the chemistry of pyrites from weakly mineralized rocks from the same area analyses of quantitative laser ablation inductively coupled plasma mass spectrometry la icp ms are processed in three distinct manners to better evaluate the trace elements controlled by silicates oxides sulfides and sulfosalt inclusions and the trace elements that are structurally bound to pyrite detailed investigation of the trace element content of pyrite indicates that most elements are controlled by silicate inclusions some reflect the composition of the host rock others correlate with the mineralizing style and only te and bi are discriminant of the porphyry systems of the chibougamau area tellurium is structurally bound to pyrite or forms telluride nanoparticles in the study area while the distribution of bi is controlled by galena and chalcopyrite inclusions and pyrite chemistry is interpreted using absolute te values and bi ratios bi pb and bi cu this study provides insight into the cu au magmatic hydrothermal systems of the chibougamau area it also has implications for the way pyrite chemistry can be used to probe for magmatic fluids in other mineralized contexts

developing a big picture of earth s mantle the sounds of distant earthquakes specially combined by large computers are producing the first global three dimensional maps of the mantle

origin of high grade gold ore source of ore fluid components and genesis of the meikle and neighboring carlin type deposits northern carlin trend nevada the meikle mine exploits one of the world s highest grade carlin type gold deposits with reserves of ca 220 t gold at an average grade of 24 7 g t locally gold grades exceed 400 g t several geologic events converged at meikle to create these spectacular gold grades prior to mineralization a devonian hydrothermal system altered the bootstrap limestone to fe rich dolomite subsequently the rocks were brecciated by faulting and late jurassic intrusive activity the resulting permeability focused flow of late eocene carlin type ore fluids and allowed them to react with the fe rich dolomite fluid inclusion data and mineral assemblages indicate that these fluids were hot ca 220 c of moderate salinity 2 s rich gold rich pyrite formed by dissolution of dolomite and sulfidation of its contained fe where dissolution and replacement were complete ore stage pyrite and other insoluble minerals were all that remained locally these minerals accumulated as internal sediments in dissolution cavities to form ore with gold grades 400 g t petrographic observations geochemical data and stable isotope results from the meikle mine and other deposits at the goldstrike mine place important constraints on genetic models for meikle and other carlin type gold deposits on the northern carlin trend the ore fluids were meteoric water d 135 18 o 5 that interacted with sedimentary rocks at a water rock ratio of ca 1 and temperatures of ca 220 c the absence of significant silicification suggests that there was little cooling of the ore fluids during mineralization these two observations strongly suggest that ore fluids were not derived from deep sources but instead flowed parallel to isotherms the gold was transported by h 2 s 34 s 9 which was derived from paleozoic sedimentary rocks the presence of auriferous sedimentary exhalative mineralization in the local stratigraphic sequence raises the possibility that preexisting concentrations of gold contributed to the carlin type deposits taken together our observations suggest that meteoric water evolved to become an ore fluid by shallow circulation through previously gold and sulfur enriched rocks carlin type gold deposits formed where these fluids encountered permeable reactive fe rich rocks

copper arsenic decoupling in an active geothermal system a link between pyrite and fluid composition abstract over the past few decades several studies have reported that pyrite hosts appreciable amounts of trace elements which commonly occur forming complex zoning patterns within a single mineral grain these chemical zonations in pyrite have been recognized in a variety of hydrothermal ore deposit types e g porphyry cu mo au epithermal au deposits iron oxide copper gold carlin type and archean lode au deposits among others showing in some cases marked oscillatory alternation of metals and metalloids in pyrite growth zones e g of cu rich as au ag depleted zones and as au ag rich cu depleted zones this decoupled geochemical behavior of cu and as has been interpreted as a result of chemical changes in ore forming fluids although direct evidence connecting fluctuations in hydrothermal fluid composition with metal partitioning into pyrite growth zones is still lacking in this study we report a comprehensive trace element database of pyrite from the tolhuaca geothermal system tgs in southern chile a young and active hydrothermal system where fewer pyrite growth rims and mineralization events are present and the reservoir fluid i e ore forming fluid is accessible we combined the high spatial resolution and x ray mapping capabilities of electron microprobe analysis empa with low detection limits and depth profiling capacity of secondary ion mass spectrometry sims in a suite of pyrite samples retrieved from a 1 km drill hole that crosses the argillic 20 450 m and propylitic 650 1000 m alteration zones of the geothermal system we show that the concentrations of precious metals e g au ag metalloids e g as sb se te and base and heavy metals e g cu co ni pb in pyrite at the tgs are significant among the elements analyzed as and cu are the most abundant with concentrations that vary from sub ppm levels to a few wt i e up to 5 wt as 1 5 wt cu detailed wavelength dispersive spectrometry wds x ray maps and sims depth vs isotope concentration profiles reveal that pyrites from the tgs are characterized by chemical zoning where the studied elements occur in different mineralogical forms arsenic and co occur as structurally bound elements in pyrite cu and au in pyrite can occur as both solid solution and submicron sized particles of chalcopyrite and native au or au tellurides respectively pyrites from the deeper propylitic zone do not show significant zonation and high cu co as concentrations correlate with each other in contrast well developed zonations were detected in pyrite from the shallow argillic alteration zone where cu co rich as depleted cores alternate with cu co depleted as rich rims these microanalytical data were contrasted with chemical data of fluid inclusions in quartz and calcite veins high cu as ratios and borehole fluid low cu as ratios reported at the tgs showing a clear correspondence between cu and as concentrations in pyrite forming fluids and chemical zonation in pyrite these observations provide direct evidence supporting the selective partitioning of metals into pyrite as a result of changes in ore forming fluid composition most likely due to separation of a single phase fluid into a low density vapor and a denser brine capable of fractionating cu and as

a carbonaceous sedimentary source rock model for carlin type and orogenic gold deposits this paper presents evidence and arguments that carbonaceous sedimentary rocks were a source for au and as in sediment hosted orogenic and carlin type gold deposits and develops a corresponding genetic model in this two stage basin scale model gold and arsenic are introduced early into black shale and turbidite basins during sedimentation and diagenesis stage 1 and concentrated to ore grades by later hydrothermal structural or magmatic processes stage 2 in reduced continental margin basin settings organic matter sedimented under anoxic to euxinic conditions immobilizes and concentrates gold arsenic and a range of trace elements particularly v ni se ag zn mo cu u present in marine bottom waters into fine grained black mudstone and siltstone of slope and basin facies during early diagenesis gold and certain other trace elements ni se te ag mo cu pge are preferentially partitioned into arsenian pyrite that grows in the muds these processes produce regionally extensive black shale and turbidite sequences enriched in syngenetic gold and arsenic commonly from 5 to 100 ppb au and 10 to 200 ppm as rare organic and sulfide rich metalliferous black shales may contain up to 1 to 2 ppm au and over 1 000 ppm as present as refractory gold in arsenian pyrite and nanoparticles of free gold during late diagenesis and early metamorphism stage 2 the diagenetic arsenian pyrite is recrystallized to form coarser grained pyrite generations and the organic matter is cooked to bitumen under higher grade metamorphism lower greenschist facies and above arsenian pyrite in carbonaceous shales is converted to pyrrhotite these processes release gold arsenic sulfur and other elements sb te cu zn mo bi tl and pb from the source rocks to become concentrated by hydrothermal processes locally to produce gold ores in structural sites such as fold hinge zones shear or breccia zones within or above the black shale sequence la icp ms analyses of diagenetic pyrite in carbonaceous sediments both associated and not associated with gold deposits suggests that invisible gold contents of greater than 250 ppb in diagenetic pyrite are indicative of carbonaceous shale source rocks with the potential to produce economic gold deposits application of this sedimentary source rock model enables a systematic exploration approach for sediment hosted gold deposits based on the distribution composition and structure of carbonaceous shale sequences and their contained diagenetic pyrite

replacement of pyrrhotite by pyrite and marcasite under hydrothermal conditions up to 220 c an experimental study of reaction textures and mechanisms the transformation of pyrrhotite to fe disulfide pyrite and or marcasite under hydrothermal conditions was studied experimentally by probing the effects of temperature up to 220 c vapor saturated pressures s ii concentrations ph and availability of oxygen on reaction progress and on the resulting textures the pyrrhotite to fe disulfide reaction proceeded by a dissolution reprecipitation mechanism under all conditions marcasite and pyrite formed under both oxic and anaerobic conditions which is inconsistent with the traditionally assumed polysulfide route for fes2 formation oxidants required for polysulfide formation the nature of the products was controlled by the level of supersaturation of the solution with respect to fe disulfide minerals marcasite formed preferentially at low ph or s ii deficient solutions saturation index 1000 different textures were obtained for the replacement of pyrrhotite by either pyrite or marcasite pyrite formation proceeded by direct replacement of pyrrhotite and simultaneously by overgrowth from solution the pyrite crystals were 10 m in size and randomly oriented in comparison marcasite crystals were 1 m in size and no significant overgrowth was observed at ph21 c 3 the marcasite nanocrystals showed the well known crystallographic relationship with pyrrhotite but at ph21 c 3 96 the marcasite crystallites were randomly oriented these experimental results confirm that the preservation of the crystallographic orientation is not a distinguishing feature between dissolution reprecipitation and solid state reactions the different textures among pyrite and marcasite reflect the dominance of crystal growth pyrite vs nucleation marcasite as a precipitation mechanism

linking high grade gold mineralization to earthquake induced fault valve processes in the porgera gold deposit papua new guinea processes responsible for high grade gold enrichment are of significant economic interest and have long been elusive structural and geophysical models postulate that earthquake induced fault valve processes are frequently responsible for gold mineralization in structurally controlled hydrothermal systems although a comprehensive geochemical record of these processes has been lacking the porgera gold deposit papua new guinea provides an opportunity to examine the complex processes surrounding high grade au mineralization in structurally controlled hydrothermal systems new high resolution trace element and sulfur isotope data obtained in situ by laser ablation inductively coupled plasma mass spectrometry and sensitive high resolution ion microprobe stable isotope analysis of pyrite across a well constrained paragenetic sequence reveal a temporal evolution in fluid chemistry the data uncover a stratigraphy of repeated high au negative 34 s and low au positive 34 s zones within individual pyrite crystals present in the highest grade gold event stage ii results provide the first clear geochemical documentation of rapid complete switching in ore forming processes preserved in individual pyrite crystals throughout an evolving hydrothermal system it is postulated that geochemical variations are attributable to rapid au deposition during pressure release due to fault failure followed by switching to more reduced rock buffered metal poor fluids from adjacent sediments as the rupture seals the cyclicity of this process is reflected in the pyrite zonation seen at the porgera deposit this study demonstrates the usefulness of applying contemporary analytical techniques to pyrite in hydrothermal systems to gain new insights into ore genesis and fluid pathways revealing that deposition of exceptionally high grade ore at the porgera deposit was the result of multiple events in a fluctuating ore forming environment

an experimental study of the mechanism of the replacement of magnetite by pyrite up to 300 c abstract we present the results of an experimental study into the sulfidation of magnetite to form pyrite marcasite under hydrothermal conditions 90 300 c vapor saturated pressures a process associated with gold deposition in a number of ore deposits the formation of pyrite marcasite was studied as a function of reaction time temperature ph sulfide concentration solid weight to fluid volume ratio and geometric surface area of magnetite in polytetrafluoroethylene lined autoclaves ptfe and a titanium and stainless steel flow through cell marcasite was formed only at ph 21 c 21 c 1 11 while pyrite predominated at ph 21 c 2 and formed even under basic conditions up to ph 21 c 12 13 marcasite formation was favored at higher temperatures fine grained pyrrhotite formed in the initial stage of the reaction together with pyrite in some experiments with large surface area of magnetite grain size 120 c 0 96 4 42 and that rate of the transformation increased from 120 to 190 c scanning electron microscope sem imaging revealed that micro pores 0 1 5 m scale existed at the reaction front between the parent magnetite and the product pyrite and that the pyrite and or marcasite were euhedral at ph 21 c 155 c 4 42 the experimental results are in good agreement with sulfide phase assemblage and textures reported from sulfidized banded iron formations pyrite marcasite and pyrrhotite have been found to exist or co exist in different sulfidized banded iron formations and the microtextures show no evidence of sub m scale pseudomorphism of magnetite by pyrite

invisible gold in arsenian pyrite and arsenopyrite from a multistage archaean gold deposit sunrise dam eastern goldfields province western australia the sunrise dam gold mine 11 1 moz au is the largest deposit in the archaean laverton greenstone belt eastern goldfields province yilgarn craton western australia the deposit is characterized by multiple events of fluid flow leading to repeated alteration and mineralization next to a major crustal scale structure the au content of arsenian pyrite and arsenopyrite from four mineralizing stages d1 d3 d4a and d4b and from different structural and lithostratigraphic environments was measured using in situ laser ablation inductively coupled plasma mass spectrometry pyrite contains up to 3 067 ppm au n 224 whereas arsenopyrite contains up to 5 767 ppm n 19 gold in arsenopyrite d4a stage was coprecipitated and remained as invisible gold nanoparticles and or lattice bound during subsequent deformation events in contrast gold in pyrite is present not only as invisible gold but also as micrometer size inclusions of native gold electrum and au ag tellurides pristine d1 and d3 arsenian pyrite contains relatively low au concentrations 26 ppm the highest au concentrations occur in d4a arsenian rich pyrite that has recrystallized from d3 pyrite textures show that this recrystallization proceeded via a coupled dissolution reprecipitation process and this process may have contributed to upgrading au grades during d4a in contrast au in d4b pyrite shows grain scale redistribution of invisible gold resulting in the formation of micrometer scale inclusions of au minerals the speciation of au at sunrise dam and the exceptional size of the deposit at province scale result from multiple fluid flow and multiple au precipitating mechanisms within a single plumbing system

global mantle flow and the development of seismic anisotropy differences between the oceanic and continental upper mantle 1 viscous shear in the asthenosphere accommodates relative motion between earth s surface plates and underlying mantle generating lattice preferred orientation lpo in olivine aggregates and a seismically anisotropic fabric because this fabric develops with the evolving mantle flow field observations of seismic anisotropy can constrain asthenospheric flow patterns if the contribution of fossil lithospheric anisotropy is small we use global viscous mantle flow models to characterize the relationship between asthenospheric deformation and lpo and compare the predicted pattern of anisotropy to a global compilation of observed shear wave splitting measurements for asthenosphere 500 km from plate boundaries simple shear rotates the lpo toward the infinite strain axis isa the lpo after infinite deformation faster than the isa changes along flow lines thus we expect the isa to approximate lpo throughout most of the asthenosphere greatly simplifying lpo predictions because strain integration along flow lines is unnecessary approximating lpo with the isa and assuming a type fabric olivine a axis parallel to isa we find that mantle flow driven by both plate motions and mantle density heterogeneity successfully predicts oceanic anisotropy average misfit 13 continental anisotropy is less well fit average misfit 41 but lateral variations in lithospheric thickness improve the fit in some continental areas this suggests that asthenospheric anisotropy contributes to shear wave splitting for both continents and oceans but is overlain by a stronger layer of lithospheric anisotropy for continents the contribution of the oceanic lithosphere is likely smaller because it is thinner younger and less deformed than its continental counterpart

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

gold and trace element zonation in pyrite using a laser imaging technique implications for the timing of gold in orogenic and carlin style sediment hosted deposits laser ablation icp ms imaging of gold and other trace elements in pyrite from four different sedimenthosted gold arsenic deposits has revealed two distinct episodes of gold enrichment in each deposit an early synsedimentary stage where invisible gold is concentrated in arsenian diagenetic pyrite along with other trace elements in particular as ni pb zn ag mo te v and se and a later hydrothermal stage where gold forms as either free gold grains in cracks in overgrowth metamorphic and or hydrothermal pyrite or as narrow goldarsenic rims on the outermost parts of the overgrowth hydrothermal pyrite compared to the diagenetic pyrites the hydrothermal pyrites are commonly depleted in ni v zn pb and ag with cyclic zones of co ni and as concentration the outermost hydrothermal pyrite rims are either as au rich as in moderate to highgrade deposits such as carlin and bendigo or co ni rich and as au poor as in moderate to low grade deposits such as sukhoi log and spanish mountain the early enrichment of gold in arsenic bearing syngenetic to diagenetic pyrite within black shale facies of sedimentary basins is proposed as a critical requirement for the later development of carlin style and orogenic gold deposits in sedimentary environments the best grade sediment hosted deposits appear to have the gold climax event toward the final stages of deformation related hydrothermal pyrite growth and fluid flow

the coupled geochemistry of au and as in pyrite from hydrothermal ore deposits the ubiquity of au bearing arsenian pyrite in hydrothermal ore deposits suggests that the coupled geochemical behaviour of au and as in this sulfide occurs under a wide range of physico chemical conditions despite significant advances in the last 20years fundamental factors controlling au and as ratios in pyrite from ore deposits remain poorly known here we explore these constraints using new and previously published empa la icp ms sims and pixe analyses of as and au in pyrite from carlin type au epithermal au porphyry cu cu au and orogenic au deposits volcanogenic massive sulfide vhms witwatersrand au iron oxide copper gold iocg and coal deposits pyrite included in the data compilation formed under temperatures from 30 to 600 c and in a wide variety of geological environments the pyrite au as data form a wedge shaped zone in compositional space and the fact that most data points plot below the solid solubility limit defined by reich et al 2005 indicate that au1 is the dominant form of au in arsenian pyrite and that au bearing ore fluids that deposit this sulfide are mostly undersaturated with respect to native au the analytical data also show that the solid solubility limit of au in arsenian pyrite defined by an au as ratio of 0 02 is independent of the geochemical environment of pyrite formation and rather depends on the crystal chemical properties of pyrite and post depositional alteration compilation of au as concentrations and formation temperatures for pyrite indicates that au and as solubility in pyrite is retrograde au and as contents decrease as a function of increasing temperature from 200 to 500 c based on these results two major au as trends for au bearing arsenian pyrite from ore deposits are defined one trend is formed by pyrites from carlin type and orogenic au deposits where compositions are largely controlled by fluid rock interactions and or can be highly perturbed by changes in temperature and alteration by hydrothermal fluids the second trend consists of pyrites from porphyry cu and epithermal au deposits which are characterised by compositions that preserve the au as signature of mineralizing magmatic hydrothermal fluids confirming the role of this sulfide in controlling metal ratios in ore systems

pyrite and pyrrhotite textures and composition in sediments laminated quartz veins and reefs at bendigo gold mine australia insights for ore genesis the various types textures and compositional zoning of pyrite in the gold bearing saddle reefs quartz veins and surrounding sedimentary rocks provide new information on the potential source and timing of gold and arsenic and related fluid processes responsible for mineralization at bendigo nodular diagenetic pyrite in the black shale tops to sandstone turbidites is enriched in invisible gold and arsenic with mean values of 0 61 ppm au 1 300 ppm as and au ag 1 based on la icpms analyses other elements enriched in the diagenetic pyrite within the organic rich shales are mn zn mo cu v ba ag cd tl co ni bi pb and te in contrast euhedral and growth zoned hydrothermal pyrite in the turbidites and bedding parallel laminated quartz veins contains lower contents of most trace elements but has higher contents of invisible au and as especially on the outermost rim of the pyrite the gold rich pyrite rims generally become thicker a few to hundreds of microns in proximity to the gold bearing saddle reefs pyrite in the reef commonly has the highest levels of invisible au and as and the lowest levels of other trace elements it is characterized by au ag 1 and au pb 0 01 in the deepest stratigraphic levels below known productive gold reefs diagenetic pyrite in the most carbonaceous shales has been replaced by pyrrhotite during metamorphism la icpms analyses reveal that the disseminated pyrrhotite contains similar levels of ni and co to the diagenetic pyrite but is strongly depleted in as and au the spatial relationships between organic rich shales folded bedding parallel laminated quartz veins and gold arsenic bearing saddle reefs combined with the consistent trends in the trace element composition of pyrite hosted by these three geological elements is interpreted to indicate that the black shales were an initial source of au and as and the laminated quartz veins acted as the initial pathways for hydrothermal fluid flow carrying au and as from the source shales to the saddle reefs maximum gold and arsenic input into the reefs principally as free gold plus arsenopyrite occurred late during deformation toward the end of the hydrothermal cycle and is expressed by the au as rich rims to hydrothermal pyrite in the sedimentary host rocks laminated quartz veins and reefs this corresponds with final fold lockup and the development of through going fault arrays linking adjacent anticlines the source of au and as for this final and most economically important fluid flow event is considered to be from carbonaceous shales deeper in the basin where original gold bearing diagenetic arsenian pyrite reacts with organic matter and is converted to pyrrhotite with release of au as and s to the metamorphic fluid

crustal deformation across and beyond the los angeles basin from geodetic measurements we combine 6 years of global positioning system gps data with 20 years of trilateration data and a century of triangulation taped distance and astronomic azimuth measurements to derive 66 interseismic station velocities in the greater los angeles region we interpolate the velocities to construct a regional strain rate map beyond the los angeles basin our results generally agree with the model proposed by the working group on california earthquake probabilities in 1995 important regional findings of this study are as follows 1 there is a significant n s convergence and e w extension about 0 22 and 0 17 0 05 strain yr respectively for the two components along the southern frontal fault system of the san gabriel mountains 2 the crustal deformation around the big bend of the san andreas fault saf cannot be explained solely by wrench style motion across the saf remaining motion could be part of a nw se extension which is the response to nfsw compression in the central transverse ranges region alternatively it could be caused by left lateral faulting on an oblique blind thrust beneath the san gabriel mountains 3 low strain rates axe found along the elsinore fault and newport inglewood 4 north south compression decreases from the raymond hill fault westward to the santa monica fault there is little east west extension along this fault system

partitioning of arsenic between hydrothermal fluid and pyrite during experimental siderite replacement abstract arsenian pyrite is the major host mineral of gold in carlin type gold deposit ctgd and forms during the interaction of h2s bearing hydrothermal fluids with fe bearing carbonates e g siderite ankerite fe rich dolomite in the wall rock experimental replacement of siderite at hydrothermal conditions i e 200 c psat was used to study the parameters that control the formation of ctgd pyrite i e ph time ah2s and the partitioning of as between the hydrothermal fluid and newly formed pyrite hydrothermal pyrite formed via replacement of siderite in experiments mainly occurs as two types 1 porous massive pyrite at alkaline ph conditions or 2 clusters of dense euhedral to anhedral pyrite grains at slightly acidic conditions ph concentration of as in newly formed pyrite depends strongly on the as concentration of the hydrothermal fluid used in the experiment calculated partition coefficients vary between 300 and 1700 with lowest d values at high as concentrations of the fluid in the studied system as 1 substitutes for s 2 as indicated by the correlation of high as with low s concentrations experimental findings agree well with previous studies in natural ctgd on as substitution and the partitioning of as between ore stage pyrite and hydrothermal fluids trapped as fluid inclusions the newly constrained partition coefficients for as help to explain the large heterogeneity in natural ctgd pyrite compositions which is caused by changes in the fluid composition due to the strong partitioning of as into the forming pyrite

involvement of anomalously as au rich fluids in the mineralization of the heilan gou gold deposit jiaodong china evidence from trace element mapping and in situ sulfur isotope composition abstract the mesozoic 120 ma heilan gou gold deposit located in the jiaodong gold province eastern margin of the north china craton ncc consists of several ultra high grade up to 600 g t auriferous quartz veins in the early cretaceous guojialing granodioritic pluton ore related pyrite crystals from this deposit show complex textures in this study emp nano sims trace element mapping and in situ sulfur isotope analyses were conducted to characterize the textural and compositional features two types of pyrite were identified type i crystals py i hosted in gold quartz pyrite veins are generally homogeneous in chemical composition they contain low concentrations of as based on the distinctive textural and compositional signatures between py iia and py iib it is proposed that anomalously as au rich fluids were injected into hydrothermal systems during the late ore forming stage which may have intensively interacted with certain sedimentary rocks the involvement of these fluids firstly documented in this study can largely explain the occurrence of native gold ore shoots at heilan gou in addition the intimate association between as and au highlights the important roles of as in enrichment of au in the jiaodong gold district

nanosims element mapping and sulfur isotope analysis of au bearing pyrite from lannigou carlin type au deposit in sw china new insights into the origin and evolution of au bearing fluids abstract sulfur isotope signatures of au bearing pyrite from lannigou au deposit a typical carlin type au deposit in sw china provide valuable information about the origin of the ore forming minerals analysis by nanosims was used to determine s isotope compositions of au bearing pyrite and to map the grain scale distributions of au cu as and s in pyrite from the deposit based on different textural pattern of pyrites revealed by back scattered electron bse images they are divided into three types py 1 diagenetic pyrite without core rim structure py 2 pyrite with an au free core and a rhythmically zoned au bearing rim py 3 au bearing pyrite with rhythmic zoning across the entire grain the element distributions and s isotope compositions of four paragenetic stages are recognized on the basis of textural observation py 1 grains and the au free homogeneous cores of zoned crystals were formed in stage 1 while the au bearing rims of the zoned crystals with rhythmic zonation of as and cu and to a lesser degree au were formed in two superimposed stages stage 2 formed the inner zone that is enriched in as alone and stage 3 formed the outer zone that is enriched in both au and as other sulfides such as realgar cinnabar and stibnite are formed in the last stage the relationship between au and as distributions in pyrite rim is complicated changing from coupled to decoupled at the nanoscale such complexity is interpreted to reflect fluctuation of fluid composition and temperature with time which in turn affect the modes of occurrence of as and au it is inferred that as mainly occurs in the crystal lattice replacing s whereas au is mainly present as nanoparticles that were trapped in pyrite during crystal growth the au bearing rims of the zoned pyrite crystals are characterized by highly variable 34s values from 1 1 to 18 1 which exceed the values of the triassic calcareous host rocks 10 14 in contrast the 34s values of the au free cores of zoned pyrite crystals vary over a narrower interval and are mainly between 6 and 12 close to the values of pyrite crystals in the sedimentary country rocks our new analyses also reveals that the 34s values of the au bearing fluids generally increase during the formation of the deposit the observed s isotope variations are consistent with mixing between a magmatic related fluid with mantle like 34s value 0 and a sedimentary or deep basin brine fluid with elevated 34s value 18 with an increasing contribution from the latter with time the notably varied values of 34s and the disseminations of au and other trace elements such as as and cu in pyrite crystals indicate that the process responsible for au precipitation in this deposit occurred in an open hydrothermal system

trace elements in fluid inclusions of sediment hosted gold deposits indicate a magmatic hydrothermal origin of the carlin ore trend the carlin type deposits in nevada western usa constitute the world9s second largest gold ore province these structurally and stratigraphically controlled sediment hosted ore bodies are characterized by carbonate dissolution attending hydrothermal precipitation of gold rich arsenian pyrite the origin of the mineralizing fluids and the source of the gold remain debated conceptual models favoring either sedimentary metamorphic or magmatic fluid sources are based on isotopic tracers giving ambiguous results here we use the trace element compositions of fluid inclusions to separate geochemical signals of the large scale fluid source from effects of deposit scale fluid interaction with the sedimentary host rocks specifically we compare the ratios of rb k b as sr and ba between clearly magmatic hydrothermal cu au ores at copper canyon in the battle mountain eureka trend with the gold quarry and chukar footwall deposits on the carlin trend that contain high grade gold in similar sedimentary host rocks results indicate that both ore districts can be related to upper crustal hydrous magmatic intrusions but are now exposed at different levels of erosion and formed at different distances from their magmatic fluid source fluid compositions are best explained by separation of a deep magmatic fluid into rb k enriched brine and b as au enriched vapor followed by cooling and contraction of the magmatic vapor phase to an epithermal liquid which reacted with sr ba bearing sedimentary rocks during ascent and eventual precipitation of au rich arsenian pyrite

the mechanics of continental transforms an alternative approach with applications to the san andreas system and the tectonics of california article i nfo displacement on intracontinental transforms is commonly distributed over a zone several hundred km wide and may incorporate large regions of transtensional and transpressional strain but no consensus exists on what controls the distribution and style of this deformation we model the transform boundary as a weak shear zone of finite length that exerts shear stress on the deformable continental lithosphere on either side strain rate decreases away from the shear zone on a scale related to its length force balance in this system requires lateral gradients in shear strain rate to be balanced by longitudinal gradients in stretching rates which create zones of lithospheric thickening and thinning distributed anti symmetrically about the shear zone simple analytical estimates two dimensional 2d spectral models and 2d 3d numerical models are employed to study the spatial scales and magnitudes of the zones of uplift and subsidence using reasonable parameter values the models yield geologically relevant rates strain rate components inferred from the gps determined 2 d velocity field and analysis of seismicity using kostrov s method taken together with the geological data on the distribution of active faults uplift and subsidence suggest that the distribution and rates of active deformation in california are consistent with our predictions this validates the assumptions of the continuum approach and provides a tool for predicting and explaining the tectonics of california and of other intracontinental transform systems