mesozoic ash flow caldera fragments in southeastern arizona and their relation to porphyry copper deposits jurassic and upper cretaceous volcanic and associated granitic rocks in southeast arizona are remnants of large composite silicic volcanic fields characterized by voluminous ash flow tuffs and associated calderas presence of 10 15 large caldera fragments is inferred primarily from 1 ash flow deposits more than 1 km thick having features of intracaldera ponding 2 exotic block breccias within a tuff matrix interpreted as caldera collapse megabreccias and 3 local granitic intrusions along arcuate structural boundaries of the thick volcanic sequences several porphyry copper deposits are associated with late granitic intrusions within the calderas or along their margins

re os isotope systematics of sulfides from felsic igneous rocks application to base metal porphyry mineralization in chile dating sulfides and determining the source of ore forming metals have been limiting factors in our understanding of processes that produce hydrothermal ore deposits here we analyze sulfides from base metal porphyry deposits from chile to demonstrate the potential of the re os system to determine both the age and the source of metals for hydrothermal mineralization cogenetic chalcopyrite bornite pyrite and sphalerite from el teniente ca 5 ma have 187 re 188 os ratios from 0 3 to 21 8 and initial 187 os 188 os ratios from 0 17 to 0 22 a paragenetically late pyrite that has an initial 187 os 188 os of 0 88 indicates that the ore deposit is not isotopically homogeneous in os throughout the formation of the deposit pyrite samples from andacollo ca 100 ma have 187 re 188 os ratios from 15 to 3600 and different isochrons yield ages between 87 and 103 ma consistent with different sericite k ar ages initial 187 os 188 os ratios of 0 2 to 1 1 are similar to those of el teniente the relatively homogeneous 187 os 188 os ratios 0 19 for cogenetic sulfides from el teniente suggest that most of the os in the ore was from the causal intrusive the latestage pyrite probably incorporated os leached from the country rock by meteoric fluids which mixed with magmatic fluids at the periphery of the hydrothermal system we demonstrate that the re os isotope system can be a powerful geochronological tool in hydrothermal ore deposits the large range in re os ratios of sulfides permits the age of mineralization to be well constrained despite isotopic heterogeneities of the hydrothermal fluids

subgrain scale decoupling of re and 187os and assessment of laser ablation icp ms spot dating in molybdenite abstract reproducibility of re os molybdenite ages depends on sample size and homogeneity suggesting that re and os are decoupled within individual molybdenite crystals and do not remain spatially linked over time in order to investigate the re os systematics of molybdenite at the subgrain micron scale we report la icp ms re os ages for an archean molybdenite crystal from aittojarvi finland analyzed in situ in a white aplite matrix a related aittojarvi molybdenite a996d in the form of a very fine grained mineral separate is used as one of our in house ntims standards and thus its age of 2760 9 ma is well established measurements of 187 re 187 os 185 re on micron scale spots along 200 m traverses across the crystal yield a wide range of ages demonstrating that in this case microsampling of molybdenite does not produce geologically meaningful ages experimentation with mineral separations and sample size over a 7 yr period predicted that this would be the outcome we suggest that 187 os is more likely to be the mobile species based on its charge and ionic radius and that 187 os becomes decoupled from parent 187 re with time on the micron and larger scale incompatible charge and ionic radius for os ions formed during reduction of molybdenite forming fluids may explain the widely observed absence of common initial os in molybdenite geologically accurate ages for molybdenite can only be obtained for fully homogenized crystals or crystal aggregates so that any post crystallization 187 re 187 os decoupling is overcome a growing number of geologically accurate id ntims 187 re 187 os ages for homogenized molybdenite suggest that postcrystallization mobility of radiogenic 187 os must be limited to within the molybdenite mineral phase we suggest that radiogenic 187 os may be stored in micron scale dislocations kink bands and delamination cracks produced by deformation and that the unusual structure and deformation response of molybdenite results in an increased chemical stability in this mineral migration of 187 os into adjacent silicate phases is highly unlikely but other contacting sulfides may take in os in an example from a proterozoic skarn deposit at pitkaranta western russia we demonstrate minor loss of radiogenic 187 os from molybdenite and a corresponding gain in adjacent chalcopyrite such that the molybdenite age is not perceptibly disturbed whereas the resulting chalcopyrite ages are impossibly old therefore it is unadvisable to perform re os analytical work on any sulfide in contact or intimate association with molybdenite in addition to large errors in the age if the isochron method is employed initial 187 os 188 os ratios could be erroneously high leading to seriously errant genetic interpretations

a detrital model for the origin of gold and sulfides in the witwatersrand basin based on re os isotopes abstract the re os systematics of gold and sulfides from the witwatersrand basin were utilized to determine whether the gold is detrital or was introduced by hydrothermal solutions from outside the basin gold from a gravity concentrate from the western areas gold plant and gold from the vaal reef have very high os concentrations of approximately 73 to 10000 ppb and 3 to 32 ppb re resulting in 187re 188os ratios of 0 010 to 0 185 the gold has subchondritic 187os 188os ratios between 0 1056 to 0 1099 and an average value of 0 1067 rhenium depletion ages trd range from 3 5 ga to 2 9 ga with a median age of 3 3 ga pyrite from the vaal reef have os concentrations ranging from 0 26 to 0 68 ppb re concentrations of 1 7 to 2 8 ppb and187re 188os ratios of approximately 14 to 87 the pyrite samples have measured 187os 188os ratios of 0 84 to 4 7 and define an isochron with an age of 2 99 0 11 ga mswd 0 77 the os isotopic data from the direct measurement of gold preclude introduction of gold to the witwatersrand basin from crustally derived metamorphic or hydrothermal fluids between 2 7 to 2 0 ga the unradiogenic 187os 188os ratios old trd ages of the western areas and vaal reef gold samples as well as the contemporaneously old age of the vaal reef pyrite are consistent with detrital deposition of gold during the formation of the witswatersrand basin the os data will allow for minor hydrothermal remobilization and or overprinting of hydrothermal gold on preexisting detrital gold grains but does not support the introduction of gold solely by hydrothermal fluids

fossil assemblages associated with submerged beachrock beds as indicators of environmental changes in terrigenous sediments examples from the gelasian early pleistocene of rhodes greece the lower pleistocene kritika member of the rhodes formation is composed of predominantly siliciclastic deposits that are sometimes intercalated with hardbottoms formed by drowning of former beachrock beds a wide variety of sclerobionts occur in this environment very different from the poorest soft bottom populations occurring in other levels of the kritika member the most characteristic abundant and frequently diverse are the encrusting forms coralline algae bivalves serpulid worms and bryozoans numerous other groups of sessile and vagile organisms are associated with these crust forming communities a number of skeletal organisms sometimes including zooxanthellate coral colonies formed small carbonate buildups on top of several beachrock beds boring organisms also occur evidence for a two step deepening succession over the previously formed beachrock is provided by palaeontological and sedimentological data the rapidly cemented sandy conglomeratic beds were first colonised by a relatively shallow water around 20 m biocoenosis of mostly encrusting organisms another association with encrusting and erect organisms was later established in a deeper environment 20 40 m a comparison with holocene beachrock occurring on the coast of rhodes was also undertaken their submerged part provided habitat for poorer but similar biotas to those occurring in the kritika member the lower pleistocene beachrock and associated organogenic fossil assemblages indicate repeated drowning episodes during deposition of the kritika member and provide help in sequence stratigraphic interpretations of these siliciclastic deposits notably they can be used as indicators of relative sea level changes

the remarkable re os chronometer in molybdenite how and why it works the re os rhenium osmium chronometer applied to molybdenite mos2 is now demonstrated to be remarkably robust surviving intense deformation and high grade thermal metamorphism successful dating of molybdenite is dependent on proper preparation of the mineral separate and analysis of a critical quantity of molybdenite unique to each sample such that recognized spatial decoupling of 187re parent and 187os daughter within individual molybdenite crystals is overcome highly precise accurate and reproducible age results are derived through isotope dilution and negative thermal ion mass spectrometry id ntims spatial decoupling of parent daughter precludes use of the laser ablation icp ms microanalytical technique for re os dating of molybdenite the use of a reference or control sample is necessary to establish laboratory credibility and for interlaboratory comparisons the rb sr k ar and 40ar 39ar chronometers are susceptible to chemical and thermal disturbance particularly in terranes that have experienced subsequent episodes of hydrothermal magmatic activity and therefore should not be used as a basis for establishing accuracy in re os dating of molybdenite as has been done in the past re os ages for molybdenite are almost always in agreement with observed geological relationships and when available with zircon and titanite u pb ages for terranes experiencing multiple episodes of metamorphism and deformation molybdenite is not complicated by overgrowths as is common for some minerals used in u pb dating e g zircon monazite xenotime nor are re and os mobilized beyond the margins of individual crystals during solid state recrystallization moreover inheritance of older molybdenite cores incorporation of common os and radiogenic os loss are exceedingly rare whereas inheritance common pb and pb loss are common complications in u pb dating techniques therefore molybdenite ages may serve as point in time markers for age comparisons

re os geochronology and systematics in molybdenite from the endako porphyry molybdenum deposit british columbia canada precise re os molybdenite ages for the endako porphyry molybdenum deposit and the nithi mountain occurrence british columbia canada yield new information on the timing of molybdenite deposition three episodes of mineralization are indicated 1 154 ma 2 148 to 146 ma and 3 145 ma re os dates agree well with new u pb and 40 ar 39 ar data from granitoids of the nithi phase 155 2 1 5 ma the endako phase 148 4 1 5 ma and a preore dike 147 4 0 6 ma and the casey phase 145 1 0 2 ma plus hydrothermal biotite 144 5 0 75 ma villeneuve et al 2001 the excellent correlation between the re os dates from molybdenite and the ages of granitoids from the area indicates a direct genetic relationship between these plutons and molybdenite mineralization these re os data also provide further insight into the systematics and robustness of re os in molybdenite the endako molybdenum deposit is the product of two episodes of mineralization both associated with moderate salinity 5 15 wt nacl equiv and high temperature 440 c fluids a third low temperature 190 300 c hydrothermal event is associated with eocene faulting selby et al 2000 the clear distinction between two of the re os molybdenite dates in the deposit and the close agreement of these dates to the ages of granitoid intrusions suggest that the re os system in molybdenite is not reset by high temperature 440 c moderate salinity hydrothermal fluids in contrast magmatic biotite in a 147 ma preore dike has a 40 ar 39 ar age of 145 ma identical to the age of the hydrothermal biotite indicating that 440 c fluids reset the ar ar system in biotite hence we interpret that the re os isotope system in molybdenite is resistant to resetting by high temperature fluids 440 c in contrast to the 40 ar 39 ar system in biotite the re os system in molybdenite is also unaffected by postore hydrothermal fluids these data show that molybdenite can provide critical information in understanding sulfide mineral deposition in ore systems which is not recorded by other isotopic systems in alteration minerals

origin of ree mineralization in the bastnas type fe ree cu mo bi au deposits bergslagen sweden the bastnas type deposits with mineral assemblages of fe oxides ca mg silicates rare earth element ree silicates ree fluorocarbonates and cu fe mo bi sulfides are associated with marble horizons in a strongly na k and or mg altered metavolcanic succession over a distance of at least 80 km in a sw ne trending zone in western bergslagen two subtypes occur 1 enriched relative to the other type in light ree lree and fe exemplified by the bastnas and rodbergsgruvan deposits and 2 enriched in heavy ree hree y mg ca and f represented by deposits in the norberg district bastnasite hosts primary fluid h2o co2 inclusions with salinities of 6 29 eq wt cacl2 and with total homogenization temperatures th tot of ca 300 400 c subtype 2 has late stage fluorite with fluid inclusions that show 1 16 eq wt nacl and th tot of ca 90 150 c molybdenite re os ages obtained from three deposits are 1 904 6 1 863 4 and 1 842 4 ma nd isotopic data from five different ree minerals yielded no defined isochron but a range in end 1 88 ga of 0 2 to 1 6 the oxygen isotope values 18osmow of dolomite and calcite from the associated ree mineralized skarn and recrystallized carbonate assemblages lie in the range 6 1 8 6 overlapping with those of the host marbles carbon isotope values 13cpdb show typical magmatic signatures of 6 7 to 4 4 while the host marbles group around ca 2 4 the sulfur isotope 34scdt values of associated sulfides range between 10 8 and 0 2 the combined evidence suggests ree mineralization beginning at 1 9 ga from mainly svecofennian juvenile magmatic 400 c fluids carrying si f cl s co2 and the ree in addition to other metals mineralization occurred through reactions with dolomitic layers in the supracrustal units coevally with regional metasomatic alteration associated with fluid circulation through an extensive active volcano plutonic complex

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

a re os isotope study of sedimentary rocks and copper gold ores from the ertsberg district west papua indonesia abstract the ores of the ertsberg district consist of both porphyry stockwork and contact controlled mineralization related to the grasberg and ertsberg intrusion centers high grade copper mineralization with gold occurs in skarns on the periphery of each of the intrusion centers the periphery mineralization includes the kucing liar skarn related ores the massive sulfide lenses on the borders of the grasberg intrusive complex and the giant skarn bodies of the deep and intermediate ore zones together with the ores of the dom complex on the margin of the ertsberg diorite the ertsberg orebody the basis of discovery of the district is a copper gold roof pendant of sedimentary strata in the diorite in order to clarify genetic and geochronologic links between the peripheral sediment hosted ore bodies and the intrusion hosted ore bodies re os isotopes of the ores and subjacent precambrian and phanerozoic crust were analyzed re os geochronology of molybdenites was used to resolve the age relationships of the ore bodies the grasberg and kucing liar molybdenites have older molybdenite mineralization ages of 2 88 0 02 ma and 3 01 0 02 ma respectively whereas the ertsberg molybdenite has a younger age of 2 54 0 02 ma these data agree with ar chronologies of the alteration associated with mineralization pollard and taylor 2000 pollard p j taylor r 2000 geochronology of intrusive rocks and cu au mineralization in the ertsberg district in proceedings of freeport institut teknologi bandung itb geological symposium bandung java pp 17 19 and also indicate that the grasberg and kucing liar molybdenites are closely similar in age and older than the ertsberg intrusive system re os data from pyrite chalcopyrite magnetite gold and the surrounding sedimentary rocks from the district define a mixing relationship between samples from the initial stockwork mineralization and peripheral ores of each intrusion center sulfide and oxide minerals from primary stockwork mineralization are isotopically homogeneous and define trends on isochron diagrams with distinct os initial ratios whereas sulfides and oxides taken from peripheral ores are isotopically heterogeneous and define trends on mixing diagrams one possible end member for the mixing is sedimentary rock surrounding the porphyries the measured os ratios of the sedimentary rocks range from 0 52 to 2 21 and overlap the os initial ratios of the sulfides and oxides sampled from both stockwork and contact mineralization the data suggest a model in which the continental crust supplied some of the os and by inference other metals during magma genesis in the lower crust and the remainder came from sedimentary rocks near the intrusion centers

geology re os age s and o isotopic composition of the lar porphyry cu mo deposit southeast iran abstract the lar porphyry cu mo deposit is located 20 km northeast of zahedan in the sistan suture zone ssz in the southeastern part of iran lar is a sub economic porphyry cu mo deposit with average grades of 0 16 cu 0 01 mo and 0 66 ppb au the cu mo mineralization developed in post collisional shoshonitic syenitic to monzonitic intrusions in an oligocene igneous complex known as the lar igneous complex lic the host and country rocks have undergone variable degrees of supergene and hypogene alteration including silicic potassic propylitic phyllic and argillic alteration the cu mo mineralization is mainly controlled by nnw striking faults and fractures and occurs as quartz veins and veinlets disseminated sulfides and stockworks the mineralization can be divided into two types hypogene and supergene hypogene mineralization is characterized by chalcopyrite pyrite bornite molybdenite and magnetite whereas supergene mineralization is characterized by enargite covellite chalcocite digenite malachite azurite and iron hydroxides sulfur isotope values for hypogene sulfides range from 0 28 to 1 76 and suggest an igneous source or mantle derived origin for sulfur the 18o values for quartz in mineralized quartz veins range from 9 6 to 11 5 these values would be in equilibrium with waters having calculated 18oh2o values of 9 3 11 2 suggesting magmatic water re os dating of two molybdenite samples from two different drill holes yields dates of 29 72 0 11 and 31 95 0 11 suggesting that the system was active for at least 2 0 m y

provenance of iron age iron in southern germany a new approach abstract ores slag and blooms from an early iron age smelting site in the black forest southern germany were analysed in view of their possible provenance in combination with products from a modern smelting experiment rather than employing lead isotope ratios like in a previous study osmium and strontium isotope ratios are used for the discussion of provenance the results of the smelting experiment with iron ores from the archaeological site and their comparison with original finds show the high potential of osmium as a tracer to determine provenance strontium may be an additional indicator but possible contaminations need to be assessed a celtic iron ingot has also been analysed to check the potential of osmium for further provenance studies

contrasting evolutions of hydrothermal alteration in quartz monzonite and quartz diorite wall rocks at the sierrita porphyry copper deposit arizona two wall rock types of contrasting chemical composition host the causative ruby star quartz monzonite porphyry intrusion and hypogene mineralization at the sierrita porphyry copper deposit vein related hydrothermal alteration in the harris ranch quartz monzonite and biotite quartz diorite wall rocks consists of several mineralogically discrete assemblages temporal evolution of different alteration assemblages was established in part using petrographic relations within and crosscutting relations among individual veins temperature and salinity characteristics of hydrothermal fluids responsible for filling of individual veins were determined using primary fluid inclusions in vein filling quartz each generation of primary vein filling introduced characteristic secondary fluid inclusions into earlier developed veins as well histograms of homogenization temperatures of primary and secondary fluid inclusions from different veins and accompanying salinity data permitted temporal correlations to be drawn between veins which either did not exhibit crosscutting relations in individual samples or which formed in different wall rocks and thus exhibited different alteration mineralogies evolution of hydrothermal activity in the area sampled commenced with potassic alteration in both quartz monzonite and quartz diorite wall rocks from 10 to 12 molal 37 41 wt nacl equivalent fluids inclusions of which homogenize by halite dissolution in the approximate temperature range 300 degrees to 370 degrees c salinities of later fluids were in the range 2 to 3 molal 10 15 wt nacl equivalent with only minor salinity variations for the remaining time span monitored by this study homogenization temperatures of primary fluid inclusions in veins formed from these lower salinity fluids began near 400 degrees c and increased initially to approximately 430 degrees c where boiling occurred the pressure defined by boiling of these fluids is about 330 bars a continuous decrease in fluid inclusion homogenization temperatures followed down to about 300 degrees c during which time deposition of quartz and k feldspar with accessory biotite and or hematite occurred in new and reopened veins in the quartz monzonite wall rock simultaneously in the quartz diorite a sequence of veins and adjacent alteration halos formed each consisting of an early assemblage of potassic affinity quartz biotite k feldspar albite which evolved to a propylitic assemblage quartz epidote chlorite as vein filling proceeded with continued cooling of the solution below about 300 degrees c muscovite took the place of k feldspar as the stable potassium bearing mineral in the quartz monzonite an analogue to this late stage quartz muscovite veining in the quartz monzonite could not be established in the quartz diorite but may consist of zeolite stilbite anhydrite the bulk of hypogene copper mineralization in both wall rock types was associated with approximately 2 molal 10 wt nacl equivalent solutions in the quartz diorite significant chalcopyrite deposition is associated with fluid inclusions homogenizing from 370 degrees down to about 320 degrees c and always occurs with the later stage propylitic minerals in each vein in the quartz monzonite wall rock chalcopyrite was deposited during the transition from potassic and into phyllic alteration fluid inclusion homogenization temperatures for this mineralization range from about 330 degrees down to 200 degrees c no primary chalcopyrite was seen to occur with earlier potassic veining formed from either high or low salinity fluids in the quartz monzonite a very late stage of deposition of chalcopyrite pyrite and minor bornite filled the center of late phyllic veins in the quartz monzonite correlated fluid inclusions have salinities from 1 to 5 molal 5 23 wt nacl equivalent and homogenization temperatures in the range 140 degrees to 160 degrees c the different alteration and sulfide mineral assemblages interpreted to have formed simultaneously in the two wall rocks of contrasting chemical character can be reasonably assigned to different chemical interactions of each rock type with similar or equivalent hydrothermal fluids

the origin of platinum group minerals from the freetown intrusion sierra leone inferred from osmium isotope systematics the origin of certain alluvial platinum group mineral pgm grains is controversial with two major proposed models one involves primary formation within ultramafic intrusions followed by weathering into laterites with no further alteration prior to alluvial concentration the other involves in addition solution of the platinum group elements pge during weathering of the ultramafic source rocks probably by organic reactions followed by the supergene growth of the macroscopic grains within laterites in order to provide further evidence concerning the formation of macroscopic m in size platinum group mineral grains the authors have studied the osmium isotope ratios in pgm grains from the freetown peninsula in sierra leone using an ion microprobe indirect isotopic evidence and modeling are required to infer their origin as no pgm grains larger than 10 mm have ever been discovered in situ within the source rocks unlike virtually all other alluvial pgm grains that have been studied the freetown ones are distinguished by 187 os 188 os ratios that are much higher than canonical mantle values and vary considerably between different grains 0 12 187 os 188 os 0 28 the 187 os 188 os ratios are with one exception the same for individual osmium rich inclusions within the platinum iron alloy host of each grain although different grains have significantly different 187 os 188 os ratios in the one significant exception there are two os ru ir alloy inclusions within a single platinum iron alloy host which have 187 os 188 os ratios that are different from each other various models are considered to explain these observations 1 the elevated osmium isotope ratios could be primary and derived from a mantle inhomogeneity such as a mantle plume 2 the intruded material with a canonical mantle signature may have reacted with the host rocks at the time of the intrusion or at a later stage during postulated metamorphic or hydrothermal activity or 3 the supergene remobilization could have modified the osmium isotope signature of the pgm interpretation of the osmium isotopes is by no means unambiguous the range of 187 os 188 os ratios is far higher than known mantle sources which combined with the grain to grain variation seems to rule out the primary formation model sr nd and o isotope evidence indicates no reaction with the host rocks during intrusion or by metamorphic or hydrothermal activity and mixing calculations show that enhancement of the radiogenic os during intrusion could only have been small the evidence points to some extremely localized process which could however have acted in two ways either a preexisting high concentration of rhenium and pge a xenolith was incorporated into the magma chamber remained essentially unmixed with the majority of the material in the chamber and after extrusion of the gabbro pge nuggets were weathered out into laterites or alternatively concentration processes within the magma chamber produced a localized concentration of rhenium possibly in copper sulfides or late magmatic iron oxides in acid intrusions which when chemically dissolved in the supergene environment precipitated pge nuggets with extremely radiogenic 187 os 188 os signatures the data presented in this paper in conjunction with work elsewhere have been used to demonstrate that the processes producing highly radiogenic 187 os 188 os signatures cannot have resulted from large scale processes and have been used to dismiss a number of previously proposed models however a resolution between the two alternative models proposed is not possible using the present data

relationships between a porphyry cu mo deposit base and precious metal veins and laramide intrusions mineral park arizona in the wallapai mining district porphyry style copper molybdenum mineralization occurs within and near laramide granitoid stocks at the center of an elongate zone of polymetallic quartz veins the principal mineralized veins form a well defined paragenetic sequence with a simplified mineralogy progressing through 1 anhydrite molybdenite am veins of quartz k feldspar anhydrite pyrite biotite molybdenite 2 quartz molybdenite qm veins with quartz molybdenite pyrite 3 anhydrite chalcopyrite ac veins containing quartz k feldspar anhydrite pyrite magnetite chalcopyrite chlorite rutile 4 quartz pyrite qp veins of quartz sericite pyrite and quartz pyrite chalcopyrite epidote chlorite and 5 polymetallic quartz pmq veins with a gangue assemblage of quartz sericite calcite kaolinite epidote chlorite and a variety of base and precious metal minerals the coexistence of vapor and liquid rich fluid inclusions in vein quartz shows that the molybdenite bearing anhydrite and quartz veins formed at 360 degrees to 410 degrees c from boiling low salinity brines chalcopyrite deposition in the anhydrite chalcopyrite veins was at 380 degrees to 420 degrees c from nonboiling brines averaging 20 equiv wt percent nacl and 25 equiv wt percent kcl the quartz pyrite veins formed at 320 degrees to 350 degrees c from brines of 1 to 13 equiv wt percent nacl the polymetallic quartz veins formed from dilute brines of 1 to 7 equiv wt percent nacl temperatures in the first stage of mineralization of the polymetallic quartz veins abruptly increased to 400 degrees to 450 degrees c in and near mineral park but declined outward to less than 300 degrees c on the district periphery in subsequent stages fluid temperatures decreased across the district to less than 200 degrees c pressures were 250 to 300 bars probably in a hydrostatic pressure regime during boiling related to molybdenite mineralization but they may have increased to about 1 100 bars lithostatic pressure during chalcopyrite deposition in the anhydrite chalcopyrite veins a depth during mineralization of 3 to 4 km is suggested copper and molybdenum mineralization occurred in a lithocap environment above a progenitor intrusion but was not directly related to the exposed ithaca peak stocks the evolution from hypersaline fluids in the anhydrite chalcopyrite veins to low salinity lower temperature fluids in the quartz pyrite veins suggests an influx of meteoric water into the waning porphyry style hydrothermal system brines up to 100 degrees c hotter appeared during the formation of the paragenetically later polymetallic quartz veins and constituted a new and much larger hydrothermal system the heat source presumably an unexposed intrusion was much larger than the porphyry style system the zonation in base metal ratios of polymetallic quartz veins is symmetrical with respect to the proposed heat source

weathering and deterioration of geotechnical properties in time of groundmasses in a tropical climate abstract weathering and degradation of slope materials govern erosion and stability of slopes over time weathering is often ignored or over simplified in engineering due to absence of time series of material properties and uncertainty on future environment the research in this paper investigates the rate of deterioration of geotechnical properties due to weathering over time after excavation of cut slopes in completely weathered material and residual soil in a tropical environment three cut slopes are studied with different excavation dates but with similar geological geotechnical and groundwater conditions identical slope aspect and land cover index and strength properties are determined by field and laboratory tests the results show that the hydro mechanical properties of completely weathered material in cut slopes evolve very rapidly to those of residual soil within time spans of 30 to 90 years in a tropical humid environment the properties reduce so much that instability of cut slopes is inevitable if this reduction is not taken into account during design and excavation of the slopes change of strength properties is around 1 1 to 1 3 pt per year from the original completely weathered material strength at the time of excavation this is based on simplified linear and logarithmic relationships the deterioration of geotechnical properties is likely the main reason for many slope failures in cut slopes after many years of stability in the research area of yen bai city in vietnam

petrogenesis of garnet two mica granites in the ruby mountains nevada garnet two mica granites of jurassic 160 3 m y and cretaceous 83 1 3 m y ages intrude amphibolite facies metasedimentary rocks of precambrian age and lower paleozoic sedimentary rocks in the northern part of the ruby mountains nevada high initial 87sr 86sr and high values of 18o for minerals suggest a dominantly sedimentary source for the magmas total rare earth contents are low and less fractionated cen ybn 10 than granitic rocks of similar composition in the sierra nevada and show a negative eu anomaly eu eu 0 57 these data are consistent with melting in the stability field of plagioclase with little contribution to the melt from refractory minerals such as zircon sphene and apatite minor euhedral garnets are manganese rich and magnesium poor al60sp34py3 6gr2 8 compared to garnet al79sp6py13gr2 in the intruded metamorphic rocks and show an increase in manganese and a decrease in calcium in the outer few microns fractionation of magnesium iron between garnet and biotite and of sodium potassium between k feldspar and plagioclase in the granites suggest submagmatic equilibration temperatures in the range of 365 to 505 c whereas oxygen isotope equilibration temperatures for two granites are higher at 480 and 570 c the compositions of the granites plot near minimum melting compositions in the water saturated quartz albite orthoclase system comparison of muscovite plus quartz stability the water saturated granite solidus and experimental garnet melt equilibria suggests pressures of crystallization no lower than about 3 5 kbar this pressure is compatible with that estimated from garnet plagioclase sillimanite quartz equilibria for the intruded metasedimentary rocks

genesis of the shangjinshan w mo polymetallic deposit in the eastern jiangnan tungsten belt evidences from geochemistry geochronology and zircon hf isotope analyses abstract the newly discovered shangjinshan w mo polymetallic deposit located at the southern anhui southeast china is a large scale skarn type tungsten polymetallic deposit according to mineral assemblages ore textures structures and superposition relationships of the mineralization three ore types have been recognized veinlet disseminated skarn the primary type quartz vein type and porphyry type the mineralized event of this deposit could be divided into four stages i the prograde skarn stage ii retrograde skarn stage iii quartz sulfide vein stage and iv quartz calcite vein stage the intrusion in the tungsten rich district of the shangjinshan is mainly composed of the granodiorite with zircon u pb ages of 138 4 1 2 ma to 136 7 1 3 ma meanwhile re os isotopic dating of five molybdenite samples yields an isochron age of 141 9 3 1 ma and a weighted average age of 139 3 1 7 ma respectively the ore forming ages are consistent with the rock forming ages within errors indicating that the w mo mineralization is genetically related to the shangjinshan granodiorite the granodiorite is i type granites characterized by metaluminous to slightly peraluminous and high k cal alkaline compositions they are also enriched in large ion lithophile elements liles and light rare earth elements lrees and depleted in high field strength elements hfses and heavy rare earth element hrees with obviously negative eu anomalies eu eu 0 50 0 84 the zircon ehf t values and two stage hf model ages tdm2 fall into the range 6 18 to 2 04 and 1 5 1 3 ga respectively the relatively low rhenium contents in molybdenite and high radioactive pb isotopes of the pyrites from stage ii indicate that the ore forming material was derived from shangjinshan granitic magmatism together with previously published data we propose that the w related granitoids in the jnb were likely generated by partial melting of the shangxi group with some additional mantle materials the granitic magmatism was caused by the asthenosphere upwelling triggered by the roll back of subduced paleo pacific plate during late jurassic to early cretaceous these granitic stocks predominately contributed to the production of skarn alteration and mineralization resulting in the giant tungsten polymetallic district in the jiangnan tungsten belt

reos dating of molybdenites from ore deposits in japan implication for the closure temperature of the reos system for molybdenite and the cooling history of molybdenum ore deposits abstract rhenium and osmium abundances were determined on molybdenites from eighteen ore deposits in japan fifteen vein type a skarn type a greisen type and a pegmatite type deposit re os ages obtained for molybdenites from northeastern central and southwestern japan are 100 130 ma 50 75 ma and ca 10 ma respectively reflecting the ages of regional igneous activities in individual areas for vein type ore deposits re os ages for molybdenites agree with rb sr whole rock ages of host granitoids while they are 3 12 ma older than k ar mineral ages of the host rocks on the other hand re os ages of molybdenites from skarn pegmatite and greisen type ore deposits agree with k ar ages of the host rocks the comparison of re os ages for molybdenites with rb sr and k ar ages of host rocks in vein type deposits suggests that re os closure temperature for vein molybdenite is close to whole rock rb sr closure temperature for host granitic rocks i e roughly estimated to be around 500 c and higher than k ar closure temperature for host granodiorites i e 230 370 c if the thermal history of vein molybdenites is essentially equivalent to that of host rocks one possible explanation for age discrepancies of 3 12 ma between re os ages for molybdenites and k ar ages for the wall rocks observed in vein type molybdenum deposits is that later thermal events after formation of molybdenum ores may reset k ar ages hydrothermal alteration might have occurred in such a temperature condition as to disturb k ar mineral systems in wall rocks and made them younger but not the re os system in molybdenite the other explanation might be that the age discrepancies correspond to a cooling interval from ca 500 to 300 c of host granitoid on the other hand the agreement of re os ages of molybdenites and k ar ages of host rocks in skarn pegmatite and greisen type deposits in this study indicates no later disturbance for k ar system in the wall rock or the rapid cooling of the ore and wall rocks after the formation of molybdenite deposits

late archean cu au mo mineralization at gameleira and serra verde carajas mineral province brazil constraints from re os molybdenite ages new re os molybdenite ages provide constraints on the timing of late archean cu au mo mineralization in the northern carajas mineral province molybdenite from the gameleira iron oxide cu au mo deposit yielded an age of 2 614 14 ma this age overlaps within its analytical error with re os ages of molybdenite from the serra verde cu au mo vein deposit 2 609 13 ma and from the nearby small garimpo fernando gold mining operation 2 592 13 and 2 602 13 ma which is probably related to the latter the geochronological data imply that the hydrothermal cu au mo mineralization in these three deposits was epigenetic and coincides with a regional tectonic regime changing from dextral transtension and clastic sedimentation at 2 7 2 6 ga to sinistral transpression and inversion at 2 6 ga previously reported stable isotope and microthermometric data are compatible with a magmatic affiliation of the cu au mo ores at gameleira and serra verde a genetic relationship of mineralization may therefore exist with 2 56 2 76 ga archean alkaline granitoids or with 2 6 2 7 calc alkaline to tholeiitic volcanic arc type magmatism

behavior of re during magma fractionation an example from volcan alcedo galapagos 1988 many applications in geo and cosmochronology and these sequences are more diycult to interpret becausemantle and crustal studies in mantle and crustal melting these materials could potentially disturb trace elementenvironments re is thought to be incompatible and os abundances from the values controlled solely by crystal

mineralogy and geochemistry of the san martin skarn deposit zacatecas the san martin skarn deposit was formed by a hydrothermal system associated with intrusion of the 46 m y old cerro de la gloria quartz monzonite stock into the middle cretaceous cuesta del cura limestone the deposit is exploited by two major mines the san martin mine extracts cu zn ag ore from veins and replacement bodies hosted by skarn and the sabinas mine extracts zn pb ag or au ore from veins hosted by skarn and recrystallized limestone horizontal metal zonation is well developed in the san martin district cu and ag correlate positively and the general pattern is cu ag cu zn zn pb with increasing distance from the intrusive contact the contents of fe cu zn and pb increase with depth within the ore zone au is farthest from the contact and occurs in veins within recrystallized limestone structural and stratigraphic controls were of major importance in localizing mineralization fractures in the cuesta del cura formation associated with laramide folding increased the permeability of the host rock the metasomatic aureole with accompanying sulfides is most extensive in the most deformed portion of the limestone chert and shale units of the cuesta del cura served as local impermeable barriers to hydrothermal fluids these units are mineralized only along fractures the vein system represents a series of intrusion related fractures that roughly parallel the intrusive contact and that served as major conduits for the ore forming fluids formation of both the vein system and sulfide hosting intercrystalline porosity in garnet skarn probably was aided by volume loss during metasomatism andraditie grandite garnet average composition ca 3 fe sub 1 5 super 3 al sub 0 5 si 3 o 12 and hedenbergitie clinopyroxene average cafe sub 0 91 super 2 mg sub 0 07 mn sub 0 02 si 2 o 6 are the dominant prograde eale silieate minerals tremolite aetinolite appears to be present as both a prograde and a retrograde phase other retrograde phases include wollastonite vesuvianite epidote and ehlorite fluorite and calcite are common and minor quartz is also present the metallic mineral assemblage is diverse and the paragenetie sequence can be divided into early intermediate and late stages the sequence consists of early arsenopyrite bornite ehaleopyrite pyrrhotite and molybdenite intermediate sphalerite with intergrowths of ehaleopyrite and galena and late tetrahedrite tennantite pyrite native silver and stibnite supergene phases include mareasite aeanthite stromeyerite and pyrargyrite deposition of grandite garnet probably was initiated by an increase in f sub o 2 and possibly decrease in f sub s 2 and took place at temperatures estimated in the range of 500 degrees to 550 degrees c garnet then became unstable relative to elinopyroxene and later eale silieate alteration products fluid inclusion evidence suggests initially highly saline fluids at least 24 wt kcl and 36 wt nacl with temperatures of major sulfide deposition starting at about 425 degrees c and declining thereafter initial values for f sub o 2 and f sub s 2 were such that metals were able to be transported as chloride complexes and sulfur was carried mainly as so 2 sulfide precipitation was probably eansed by a continuing decrease in temperature and an increase in ph brought about by dissolution of caco 3 local endoskarn formation and noneconomic mineralization of the intrusion preceded exoskarn formation values for x sub co 2 in the hydrothermal fluids were low or 0 05 throughout cale silieate metasomatism and sulfide deposition relative metal solubilities were the major control on metal zonation the cu ag association is a product of thermal collapse of the mineralizing system resulting in low temperature mineral assemblages coexisting with high temperature assemblages near the intrusive contact

the study of molybdenites through the187re 187os chronometer we determined the re and os concentrations in 11 molybdenites of various ages 30 2700 m y and from various areas no common osmium has been detected and os was found to be purely radiogenic therefore by comparing the concentrations we were able to determine 187 re 187 os ages for most samples these ages are in good agreement with those measured in surrounding rocks and probably correspond to the age of mineralization however two or three re os ages seem unreliable being probably related to some rhenium leaching through later metamorphic and or hydrothermal events this shows that the petrographic characteristics of ores and the type of crystallization of mos 2 are important in choosing samples suitable for dating re and os determinations combined with careful petrographic investigations may give important clues on the genesis and evolution of molybdenum ores

unraveling the origin of the andean iocg clan a re os isotope approach the andean iocg clan in the coastal cordillera of northern chile comprises the iron oxide cu au sensu stricto the iron oxide apatite ioa and the stratabound cu ag deposits also known as manto type cu ag deposits iocgs and manto type deposits constitute the second source of copper in chile after porphyry cu mo systems whereas ioas are an important source of iron regardless of their economic importance little is known about their formation and contrasting genetic models have been proposed i e an origin from magmatic hydrothermal fluids exsolved from a cooling intrusion or formation from non magmatic basinal brines heated by plutonic bodies here we report re os data for five iocg deposits candelaria mantoverde casualidad diego de almagro and barreal seco three ioas los colorados el romeral carmen and two manto type deposits altamira and franke calculated re os ages for some of these deposits are consistent with previously published geochronological data and indicate an early to late cretaceous age the calculated ages for the altamira manto type cu deposit yield a 90 ma age indicating that the cretaceous manto type cu belt of central chile extends further north than previously thought additionally the calculated initial os ratios using reported ages show that iocgs have a more radiogenic signature 2 0 2 4 than ioas 1 0 1 2 and manto type cu deposits 1 1 a comparison with previously published os initial ratios for the mantoverde 0 2 and candelaria 0 4 iocgs suggests that the mineralization in chilean iocgs is the result of different events with metals derived from diverse sources i e the magmatic hydrothermal system and basement host rocks rhenium and os concentrations for the various studied deposits vary over a wide range of values at the ppb and ppt level respectively with many sulfides and magnetite bearing appreciable no common os the re and os contents in sulfides pyrite chalcopyrite from iocgs are low ranging from 2 to 149 ppb re and up to 49 ppt os pyrite from ioa deposits show re and os concentrations ranging from 10 8 to 214 ppb re and os 156 ppt whereas magnetite has lower re and os contents 0 7 129 ppb re 0 2 3 6 ppt os however rhenium and os concentrations in magnetite might be attributed to small sulfide inclusions chalcocite from manto type cu deposits shows the widest range and highest re and os concentrations 15 to 253 ppb and 34 to 639 ppt respectively the os present in all these deposits is dominated by radiogenic 187os a comparison of re and os data from different deposit types show that andean iocg and ioa deposits have similar characteristics to chilean porphyry cu mo systems with low to moderate re content 90 osr and variable initial os ratios our data supports the idea that andean iocg and ioa deposits formed by magmatic hydrothermal processes with little involvement of basinal brines in contrast published re os information from iocgs in china and australia argue for the involvement of a much more radiogenic crustal source possibly related to non magmatic oxidized saline brines that leached basement rocks we conclude that andean iocg and ioa deposits in northern chile were formed mainly by magmatic hydrothermal processes related to the formation and emplacement of plutonic rocks with moderate contribution from leaching of basement and or volcanic host rocks surface or basin derived brines as well as sediments appear to play only a minor role in the formation of the chilean iocg clan

structural reinterpretation of the ajo mining district pima county arizona based on paleomagnetic and geochronologic studies the ajo mining district of southern arizona is divided into two main structural blocks by the gibson arroyo fault the eastern camelback mountain block contains the late cretaceous early tertiary porphyry copper deposit which has been previously thought to be associated with the displaced apex of a large intrusion exposed by deeper erosion in the western cardigan peak block however unpublished u pb data support a mid tertiary age for the western intrusion paleomagnetic and geologic evidence indicates that the ore deposit has been tilted to the south a total of approximately 120 degrees 68 degrees before and another 55 degrees after emplacement of the overlying locomotive fanglomerate and ajo volcanics the ajo volcanics have k ar ages 24 25 m y slightly older than those from the large intrusion of the cardigan peak block 20 23 m y paleomagnetic directions are consistent with the southward tilting of the volcanic rocks but they suggest that the remanent magnetization and perhaps the k ar dates of the western intrusion were reset by the emplacement of dikes younger than the locomotive fanglomerate and ajo volcanics these and other geologic relations indicate the following sequence of mid tertiary events in the district 1 emplacement of the western intrusion 2 movement along the gibson arroyo fault 3 unroofing and perhaps tilting of the pluton asymp 70 degrees to the south along with the camelback mountain block 4 syntectonic depositions of the locomotive fanglomerate and the ajo volcanics 5 continued uplift and tilting to the south totaling 40 degrees to 60 degrees 6 intrusion of the youngest dikes with attendant alteration and remagnetization of the host rocks and 7 minor oblique movement along the gibson arroyo fault

assessment of the 187re decay constant by cross calibration of re os molybdenite and u pb zircon chronometers in magmatic ore systems the past decade has seen renewed interest in 187re 187os geochronology using a variety of matrices including sulfide minerals shales and meteorites the most widely used value of the 187re decay constant 187re is 1 666 0 005 10 11 a 1 0 31 which is based on cross calibration of re os and pb pb chronometers for certain meteorites smoliar m i walker r j and morgan j w 1996 re os isotope constraints on the age of group iia iiia iva and ivb iron meteorites science 271 1099 1102 however other recent studies have yielded alternate values of 187re based upon either direct counting experiments or analysis of meteorites here we provide an independent assessment of 187re using methodology sample materials and preparation of os standard solutions different from those of smoliar et al 1996 combining re os age data for molybdenite formed in magmatic ore deposits with the u pb zircon age of the magmatic rocks a refined 187re value is determined by averaging 11 individual cross calibration experiments spanning ca 2700 ma of earth history using the u decay constants of jaffey jaffey a h flynn k f glendenin l e bentley w c and essling a m 1971 precision measurement of half lives and specific activities of 235u and 238u phys rev 4 1889 1906 a value for 187re of 1 6668 0 0034 10 11 a 1 is determined using the 238u value of jaffey et al 1971 and 235u value of schoene schoene b crowley j l condon d j schmitz m d and bowring s a 2006 reassessing the uranium decay constants for geochronology using id tims u pb data geochim cosmochim acta 70 426 445 a value for 187re of 1 6689 0 0031 10 11 a 1 is determined these values are nominally higher ca 0 1 and ca 0 2 than the value determined by smoliar et al smoliar m i walker r j and morgan j w 1996 re os isotope constraints on the age of group iia iiia iva and ivb iron meteorites science 271 1099 1102 but within calculated uncertainty further refinement of 187re by cross calibrating the molybdenite and u pb zircon chronometers should be possible by utilizing high precision single grain chemical abrasion zircon u pb analyses

re os isotopic dating of molybdenites in the xiaoliugou w mo deposit in the northern qilian mountains and its geological significance abstract the xiaoliugou is a large scale w mo deposit newly explored in the northern qilian mountains caledonian fold belt northwestern china it is a vein and skarn type deposit genetically associated with the xiaoliugou caledonian granodiorite stock re os isotopic dating for the molybdenite in the deposit yields an isochron age of 462 13 ma 2 and model ages of 436 to 496 ma these results suggest that w mo mineralization occurred before the collision of plates and mineralized substances mainly originated from the crust

the 190pt 186os decay system applied to dating platinum group element mineralization of the bushveld complex south africa abstract we evaluate the 190pt 186os decay system measured by laser ablation mc icpms as a useful geochronometric tool for direct dating of platinum group minerals pgm in large mafic ultra mafic intrusions by analysing mineralised rocks from the geochronologically well constrained bushveld complex s africa mixed pgm laurite cooperite laurite platarsite sperrylite and pt fe alloy from the merensky reef yield a pt os isochron age of 1995 50 ma 2 n 48 mswd 1 16 initial 186os 188os 0 119819 0 000006 while this is 59 myr younger than the u pb zircon age for the merensky reef scoates and friedman 2008 it is consistent with recent re os ages for the platreef considering the younger age recorded by both re os and pt os systems we propose that the pt os isochron age records a late low temperature hydrothermal event affecting pgm and sulphides in the platreef and merensky reef pt rich phases may also yield single grain 190pt 186os model ages since initial 186os 188os can be well constrained a pt os model age of 2024 ma 101 ma was calculated for a merensky cooperite a pt fe alloy from the onverwacht pipe and a tweefontein hill sperrylite give pt os model ages of 2113 106 ma and 2042 102 ma respectively a pt os isochron derived from all bushveld units gives an age of 2012 47 ma 2 186os 188osi 0 119818 0 000006 with an mswd of 1 19 hence pge mineralisation in different stratigraphic horizons of the complex cannot be distinguished temporally using the pt os chronometer nonetheless the potential for the pt os system in dating events in pge mineralised systems is evident and the agreement of single grain model ages in high pt os phases with the pt os and re os isochron ages indicates their usefulness in the geochronology of these systems

contrasting meteoritic signatures within the clearwater east and clearwater west impact structures the view from osmium isotopes abstract osmium isotopes provide a powerful tool for identifying meteoritic signatures in impactites we apply the osmium isotope method to impact melt and country rocks from the clearwater east and clearwater west craters located in quebec canada impact melts from clearwater east have 187 os 188 os ratios of 0 1281 0 1285 these values indicate a significant meteoritic component which exceeds that in impact melts at all terrestrial craters studied to date except morokweng such findings align with earlier results from chromium isotopes and platinum group elements in contrast impact melts from clearwater west have 187 os 188 os ratios between 6 604 and 59 12 these highly radiogenic ratios are indistinguishable from the 187 os 188 os ratios in country rocks hence osmium isotopes provide no evidence for a meteoritic component in impact melts at clearwater west the clearwater craters formed in almost identical targets therefore target effects cannot readily explain the stark difference between the two clearwater craters if melt sheet heterogeneity is similar at the two craters the probability that melts at clearwater west host an undetected chondritic component is 1 may best explain the unusually strong meteoritic signature although the signature or its nondetection at each crater may be related to asymmetric preservation of the impactor component the results presented here provide further evidence that clearwater east and clearwater west were temporally separate impact events

rhenium osmium evidence for regional mineralization in southwestern north america more than 40 base metal porphyry ore deposits in southwestern north america are associated with the laramide orogeny about 90 million to 50 million years ago rhenium osmium dates on molybdenite a rhenium enriched sulfide common in many of the deposits reveal that in individual deposits mineralization occurs near the final stages of magmatic activity irrespective of the time of inception magnitude or duration of magmatism deposits that differ widely in location and in the extent and timing of magmatism have nearly identical ages for mineralization rhenium osmium ages suggest that mineralization occurred during two distinct intervals from about 74 million to 70 million years ago and from 60 million to 55 million years ago most deposits that formed in the oldest interval are within the older precambrian basement of northwestern arizona whereas the younger deposits are restricted to the younger precambrian basement in southern arizona and northern mexico synchronous widespread mineralization indicates that similar crust mantle interaction occurred on a regional scale for ore deposits once thought to be the product of localized processes

rhenium and osmium isotopes in black shales and ni mo pge rich sulfide layers yukon territory canada and hunan and guizhou provinces china rhenium and osmium abundances and osmium isotopic compositions were determined by negative thermal ionization mass spectrometry for samples of devonian black shale and an associated ni enriched sulfide layer from the yukon territory canada the same composition information was also obtained for samples of early cambrian ni mo rich sulfide layers hosted in black shale in guizhou and hunan provinces china this study was undertaken to constrain the origin of the pge enrichment in the sulfide layers samples of the ni sulfide layer from the yukon territory are highly enriched in re os and other pge with distinctly higher re 192os but similar pt re compared to the black shale host re os isotopic data of the black shale and the sulfide layer are approximately isochronous and the data plot close to reference isochrons which bracket the depositional age of the enclosing shales samples of the chinese sulfide layers are also highly enriched in re os and the other pge re 192os are lower than in the yukon sulfide layer re os isotopic data for the sulfide layers lie near a reference isochron with an age of 560 ma similar to the depositional age of the black shale host the osmium isotopic data suggest that re and pge enrichment of the brecciated sulfide layers in both the yukon territory and in southern china may have occurred near the time of sediment deposition or during early diagenesis during the middle to late devonian and early cambrian respectively

preservation of re os isotope signatures in pyrite throughout low t high p eclogite facies metamorphism pyrite in lt hp eclogites from the western tianshan orogenic belt yields a re os age of 378 1 8 9 ma which is 30 70 ma older than ages previously obtained for the same rocks using the rb sr sm nd ar ar u pb and lu hf isotope systems the tianshan lt hp eclogite experienced temperatures of up to 570 c combined with pressures of up to 2 1 gpa during metamorphism these conditions are below the transition of pyrite to pyrrhotite which defines both pyrite stability and possibly its closure temperature for re os pyrite can preserve re os signatures through eclogite facies peak metamorphic conditions and thus allow determination of the formation age of pyrite in the protolith

trace element heterogeneity in molybdenite fingerprints stages of mineralization abstract variations in molybdenite trace element chemistry represent a tool for discriminating discrete events in young magmatic hydrothermal systems and constrain the role of granites in older greenstone belt hosted gold systems we show that besides re and w typical lattice bound elements molybdenite also concentrates chalcophile elements with chalcogenide affinity such as bi pb and te ces elements from the latter group form nano to micron scale inclusions which also attract au and ag incorporation high concentration of all elements is attributable to lattice defects and coherent intergrowths between molybdenite and ce minerals rather than polytypism if both groups are used trace element patterns are useful for interpreting superimposed ore forming processes we test the validity of this hypothesis by carrying out laser ablation inductively coupled mass spectroscopy spot analysis and element mapping on high re molybdenite from the tertiary au deposit at hilltop nv usa and the archean boddington cu au deposit western australia whereas w and ces are affected by both deformation and interaction with subsequent fluids re is only affected by the latter an epithermal overprint at hilltop recorded in a grain with a ce rich halo surrounding a core with re w oscillatory zoning upgrades re content and is also traceable by measurable au at boddington granite derived fluids dilute re in precursor molybdenite but both granite and orogenic deformation assist ce mineral coarsening and au release

variation of mo isotopes from molybdenite in high temperature hydrothermal ore deposits measurable molybdenum isotope fractionation in molybdenites from different ore deposits through time provides insights into ore genesis and a new technique to identify open system behavior of re os in molybdenites molybdenite samples from six porphyry copper deposits one epithermal polymetallic vein deposit four skarns and three fe oxide cu au deposits were analyzed the 97mo where open image in new window for all samples varied from 1 34 0 09 to 0 26 0 04 this is the largest molybdenum isotopic variation in molybdenite from high temperature ore deposits recorded to date 97mo of molybdenite varies as a function of the deposit type and the rhenium and osmium concentrations of the samples isotope values for mo also vary within the individual deposits in general molybdenites from porphyry copper deposits have the lightest values averaging 0 07 0 23 1 molybdenites from the other deposit types average 0 49 0 26 1 the variations could be related to the fractionation of mo into different mineral phases during the ore forming processes a comparison of the mo isotope ratios and the re os ages obtained from the same aliquot may possess a geochronological evaluation tool samples that yielded robust ages have different mo isotopic compositions in comparison to samples that yielded geologically unreasonable ages another observed relationship between the re os and mo isotope data reveals a weak correspondence between re concentration and mo isotope composition molybdenites with higher concentrations of re correspond to lighter mo isotope values

rhenium behavior in molybdenite in hypogene and near surface environments implications for re os geochronometry abstract rhenium is concentrated mainly in molybdenite mos2 and occurs as a major cation in only a few rare minerals this affinity makes molybdenite an ideal mineral for re os geochronometry but research on the behavior of re in molybdenite is limited infrared microscope xrd back scattered electron bse and microprobe techniques have been used in this study to document re behavior in molybdenite affected by hypogene and near surface processes in the hypogene environment both 3r and 2h molybdenite can experience re loss during hydrothermal alteration which also causes increased infrared transparency ir alteration at temperatures as low as 150 c can cause re loss in the presence of advecting fluids and will affect re os dating if it occurs long after primary mineralization re loss in 3r and 2h molybdenite under supergene conditions does not increase ir transparency rhenium is not incorporated into supergene ferrimolybdite but is enriched in k al silicate intergrowths which may be illite these minute intergrowths are present in several samples and would not be detected in a simple optical examination in the supergene environment elemental os is stable whereas re is not rhenium in molybdenite may be removed by supergene fluids after some has decayed to 187os causing erroneously old ages or it may be adsorbed into the illite intergrowths creating ages which are too young in the weathering environment proterozoic molybdenites have altered to re enriched powellite which can be detected using back scattered electron imagery combined microprobe xrd bse and infrared microscopy can be successfully used to detect alteration in molybdenite prior to dating these techniques are non destructive and should be performed before any molybdenite is dated by the re os system

temporal spatial distribution and tectonic setting of porphyry copper deposits in iran constraints from zircon u pb and molybdenite re os geochronology abstract porphyry copper deposits pcds in iran are dominantly distributed in arasbaran nw iran the middle segment of the urumieh dokhtar magmatic arc udma and kerman central se iran with minor occurrences in eastern iran and the makran arc this paper provides a temporal spatial and geodynamic framework of the iranian porphyry cu mo au systems based on geochronologic data obtained from zircon u pb and molybdenite re os dating of host porphyritic rocks and molybdenites in 15 major pcds the dating results define a long metallogenic duration 39 6 ma and suggest a long history of tectonic evolution from the accretionary orogeny related to early cenozoic closure of the neo tethys ocean to subsequent collisional orogeny for the iranian porphyry copper systems the oldest porphyry mineralization occurred in the eastern part of iran after the closure of a branch of the neo tethyan sistan ocean between the lut and afghan blocks in the late eocene 39 37 ma this was followed by mineralization in the kerman porphyry copper belt over a time interval of about 20 m y where two metallogenic epochs have been recognized including late oligocene 29 27 ma and miocene 18 6 ma the bondar e hanza deposit formed in the late oligocene while and the remaining dated deposits belong to miocene epoch according to the deposits characteristics and their ages the miocene epoch can be divided into early middle and late stages the darreh zar bakh khoshk chah firouzeh and sar kuh deposits formed during the early middle miocene the largest porphyry deposits occur in the middle stage during the middle miocene 14 11 ma and include the sar cheshmeh meiduk dar alu and now chun deposits these deposits were formed during crustal thickening uplift and rapid exhumation of the belt the final stage of porphyry mineralization occurred during the late miocene 9 6 ma and formed the iju kerver kuh panj and abdar deposits there were two porphyry mineralization stages in the arasbaran porphyry copper belt in nw iran including an older late oligocene 29 27 ma and a younger early miocene 22 20 ma events the haft cheshmeh deposit belongs to the older stage and the world class sungun and masjed daghi deposits formed during the early miocene in the middle segment of the udma saveh yazd porphyry copper belt pcds formed during middle miocene time 17 15 ma the geochronological results reveal that the porphyry mineralization moved from the northwest to southeast of udma over the time our dating results combined with the possible late eocene oligocene timing for collision between the arabian and iranian plates support a model for iranian pcd formation by partial melting of previously subduction modified lithosphere in a post subduction and post collisional tectonic setting

trace element geochemistry of molybdenite from the shapinggou super large porphyry mo deposit china abstract the shapinggou deposit located in the dabie orogenic belt eastern china is one of the largest mo only porphyry deposits in the world alteration types associated with shapinggou include silicic potassic silicic phyllic propylitic and argillic the phyllic alteration can be subdivided into quartz and sericite mainly muscovite phases whereas the argillic alteration is distinguished by poorly crystallized kaolinite kaolinite px muscovite and phengite the ore forming event can be divided into quartz k feldspar quartz molybdenite quartz sericite and quartz fluorite gypsum stages with molybdenite deposited in the first three stages but mainly in the second the molybdenites in shapinggou represent either the 2h1 and or the 2h1 3r polytype and can be subdivided into two groups group one and group two group 1 is associated with stage 1 alteration whereas group 2 is found with stages 2 and 3 there is an increase in the re values from group one to group two with the re contents likely controlled by both the crustal metal source and temperature with decreasing temperature the contents of re and the ratios of mo cu in molybdenites in shapinggou decrease gradually whereas the contents of cu and w sn and the ratios of re cu co ni increase the pb zn values in molybdenite are higher in the porphyry mo deposit associated with pb zn deposits than in porphyry cu mo mo deposits not associated with pb zn deposits the ratios of cl f so2 h2s and h k in the shapinggou fluids increasing over time suggest that the fluids became more oxidised the initial ore forming fluid was 500 c carried ions of mo ca na k cl f s and caused potassic silicic alteration with deposition of only small amounts of molybdenite as the temperature dropped down to 400 c the amounts of mo k cu and cl ions in the fluid decreased leading to silicic sericitic and propylitic alteration and the deposition of the majority of the molybdenite as the temperatures decreased to 300 c the fluid contained ions of ca and f and pb zn was deposited distally around the main mo ore body