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

new 40ar 39ar dating of the antrim plateau volcanics australia clarifying an age for the eruptive phase of the kalkarindji continental flood basalt province the kalkarindji flood basalt province of northern australia erupted in the mid cambrian today the province consists of scattered volcanic and intrusive suites the largest being the antrim plateau volcanics apv in northern territory accurate dating of the kalkarindji flood basalt province has proved challenging with previous studies focused on minor volcanic rocks and intrusive dykes in northern territory and western australia these previously published data corrected to the same decay constants range from 512 8 to 509 6 2 5 ma 2 placing the kalkarindji flood basalt province in apparent synchronicity with the cambrian stage 4 5 biotic crisis at 510 1 ma this study utilizes 40ar 39ar dating of basalts from the apv to accurately date the major volcanic eruptions in this province the results yield an age of 508 0 498 3 5 5 ma 2 indicating that the apv is younger than the intrusive rocks these dates allude to a relative timing discrepancy where intrusive activity in the north australian craton preceded the eruption of the apv as the last magmatic activity in the region the determination of these largest eruptions to be later than 510 ma effectively disassociates the kalkarindji lavas from being a major cause of the 510 ma biotic crisis but cannot definitively discount any deleterious effects on the fragile cambrian ecosystem supplementary material 40ar 39ar analysis data tables xrf geochemical data alteration study and photomicrographs of all five samples are available at https doi org 10 6084 m9 figshare c 4176674

gold and tin mineralisation in the ultramafic hosted cheoeum vent field central indian ridge the cheoeum vent field cvf is the first example of an inactive ultramafic hosted seafloor massive sulphide sms deposit identified in the middle part of the central indian ridge here we report on the detailed mineralogy and geochemistry of ultramafic hosted sulphide sample atop a chimney together with a few small fragments hydrothermal chimneys are characterised by high concentrations of au up to 17 8 ppm and sn up to 1720 ppm the sulphide mineralisation in the cvf shows 1 early precipitation of anhedral sphalerite and pyrite marcasite aggregates under relatively low temperature 250 c fluid conditions 2 intensive deposition of subhedral pyrrhotite isocubanite chalcopyrite fe rich sphalerite sp iii and electrum from high temperature 250 365 c and reduced fluids in the main mineralisation stage and 3 a seawater alteration stage distinguished by the mineral assemblage of marcasite pseudomorphs altered isocubanite phase covellite amorphous silica and fe oxyhydroxides electrum 2 m in size is the principal form of au mineralisation and is mainly associated with the main mineralisation stage the consistently high fineness of electrum 801 to 909 is indicative of the selective saturation of au over ag in the fluid during high temperature mineralisation which differs from the au mineralisation associated with typical basaltic hosted hydrothermal systems on mid ocean ridges tin is mainly substituted in structures of sphalerite isocubanite and chalcopyrite as a solid solution and not as mineral inclusions the continuously ascending hydrothermal fluids enable the early formed sn bearing sulphide to be dissolved and reprecipitated producing significantly sn enriched replacement boundaries between isocubanite and sp iii this study suggests that au sn mineralisation could be facilitated by the low redox potential of ultramafic hosted hydrothermal systems such as in the cvf which may be a common occurrence along slow spreading mid ocean ridges

sulfide remobilization during low temperature alteration of seafloor basalt abstract the behavior of sulfide minerals during the physical and chemical changes accompanying seafloor alteration was studied in three basalt flows from the bottom of d s d p hole 418a leg 53 the rocks are mildly altered and contain primary authigenic and vein sulfide minerals sulfide habit mineralogy and trace element content are inter related and are correlated with the extent and type of silicate and oxide alteration incipient alteration at 90 100 c was accompanied by low temperature reequilibration of pyrrhotite and locally by the oxidation of pyrrhotite to pyrite plus magnetite the dominant stage of alteration at 90 c is characterized by dissolution and local redistribution of pyrite and chalcopyrite whose precipitation appears to be controlled by the water rock ratio and the extent to which the water has been modified by reaction with the basalt chalcopyrite was concentrated relative to pyrite by slight changes in fluid composition caused by reaction with other minerals concurrent precipitation of smectite causes a net increase in rock volume tending to restrict seawater access calculations of rock cooling rate through time suggest that the most prolonged hydrothermal circulation occurs at low temperatures giving rise to pervasive low temperature alteration assemblages

unraveling the mineralogical complexity of sediment iron speciation using sequential extractions author s slotznick sp sperling ea tosca nj miller aj clayton ke van helmond nagm slomp cp swanson hysell nl abstract 2019 american geophysical union all rights reserved iron speciation is one of the most widely applied proxies used to reconstruct oxygen levels and redox conditions in past aqueous environments the iron speciation proxy estimates proportions of different reactive iron species in fine grained sedimentary rocks which are mapped to redox conditions based on empirical calibrations from modern sediments it is based on a standardized extraction technique of sequentially applying acetate hydroxlamine hcl dithionite and oxalate solutions to a powdered sample in order to dissolve iron phases and quantify the amount of iron carried by carbonates easily reducible oxyhydroxides ferric iron oxyhydr oxides and magnetite respectively although tested on pure minerals and mixtures assessments of whether this sequential extraction process accurately dissolves the targeted minerals in natural sediments and sedimentary rocks are lacking in our study residues from each sequential extraction step were analyzed using rock magnetic and x ray diffraction experiments to identify and quantify the iron bearing minerals that were dissolved the dithionite extraction robustly removes the targeted mineralogy as magnetic data show it to solubilize nearly all of the goethite however magnetic quantification of magnetite was orders of magnitude less than the iron measured in the oxalate extraction x ray diffraction data suggest that dissolution of iron bearing clays specifically berthierine chamosite could explain this disparity our data compilation shows higher values of iron from the oxalate extraction in precambrian sedimentary rock samples suggesting a significant temporal shift in iron cycling recognition of heterogeneity in chemical extraction efficiency and targeting is vital for holistic multiproxy interpretation of past oxygen levels and communication between disciplines

variable defect structures cause the magnetic low temperature transition in natural monoclinic pyrrhotite non stoichiometric monoclinic 4c pyrrhotite fe7s8 is a major magnetic remanence carrier in the earth s crust and in extraterrestrial materials because of its low temperature magnetic transition around 30 k also known as besnus transition which is considered to be an intrinsic property this mineral phase is easily detectable in natural samples although the physical properties of pyrrhotite have intensively been studied the mechanism behind the pronounced change in magnetization at the low temperature transition is still debated here we report magnetization experiments on a pyrrhotite crystal fe6 6s8 that consists of a 4c and an incommensurate 5c superstructure that are different in their defect structure the occurrence of two superstructures is magnetically confirmed by symmetric inflection points in hysteresis measurements above the transition at about 30 k the disappearance of the inflection points and the associated change of the hysteresis parameters indicate that the two superstructures become strongly coupled to form a unitary magnetic anisotropy system at the transition from this it follows that the besnus transition in monoclinic pyrrhotite is an extrinsic magnetic phenomenon with respect to the 4c superstructure and therefore the physics behind it is in fact different from that of the well known verwey transition

sulfide mineralogy in the polymetallic cassiterite deposits of dachang p r china several important mineral deposits of sn zn cu pb and other metals associated with devonian sediments and yanshanian cretaceous granitic rocks are known in the dachang district guangxi early genetic hypotheses related the origin of the deposits entirely to the yanshanian granites recently it was suggested that in devonian times an earlier syngenetic metal concentration may have occurred later overprinted by the yanshanian metallogeny this contribution is aimed at placing constraints on the physicochemical conditions during the yanshanian ore formation remobilization by studying the sulfide chemistry arsenopyrite sphalerite stannite and fluid inclusion data on the two major deposits in the area i e the polymetallic cassiterite deposit of changpo and the zn cu skarn deposit of lamo sphalerite and arsenopyrite are quite abundant in both deposits stannite is minor but fairly widespread at changpo and quite rare at lamo they are accompanied by pyrite pyrrhotite galena chalcopyrite cassiterite fluorite and a large variety of other sulfides and sulfosalts the main compositional data for sphalerite and arsenopyrite are summarized as follows

the mineralogy and crystallography of pyrrhotite from selected nickel and pge ore deposits the nonstoichiometric sulfide pyrrhotite fe s common to many ore deposits occurs in a variety of crystallographic forms and compositions and occasionally is also intergrown with stoichiometric troilite fes in this study the mineralogy of pyrrhotite derived from several different nickel and pge ore deposits in south africa botswana and canada was examined in detail in terms of pyrrhotite association crystallography and mineral chemistry pyrrhotite samples were subdivided into two phase 6c fe11s12 pyrrhotite intergrown with2c fes troilite two phase 4c fe7s8 pyrrhotite intergrown with 5c fe9s10 pyrrhotite single phase 5c fe9s10 pyrrhotite and single phase 4c fe7s8 pyrrhotite none of the pyrrhotite samples analyzed were classified as two phase 4c pyrrhotite intergrown with pyrite due to the scarcity of pyrite in these samples average solid solution ni contents of nc pyrrhotite 0 75 0 10 wt ni in this study were found to be greater than in 4c pyrrhotite 0 43 0 10 wt ni but only when the pyrrhotite occurred as two phase 4c pyrrhotite intergrown with nc pyrrhotite for single phase pyrrhotite occurrences in this study 4c pyrrhotite was more ni rich up to 2 wt ni than nc pyrrhotite 0 75 0 19 wt ni the average atomic metal s ratios obtained for 4c fe7s8 pyrrhotite was 0 869 0 013 n 699 for 5c fe9s10 pyrrhotite was 0 895 0 013 n 316 and for 6c fe11s12 pyrrhotite was 0 918 0 017 n 101 the histogram comparing metal s ratios of all the pyrrhotite samples analyzed showed a continuum of metal s ratios although with frequency maxima corresponding to the ideal compositions of 4c 5c and 6c pyrrhotite the presence of the continuum however was interpreted to be representative of nonstoichiometry in the pyrrhotite structure

iron deficiency in pyrrhotite of suevites from the chesapeake bay impact crater usa a consequence of shock metamorphism abstract pyrrhotite from suevite of the 35 ma chesapeake bay impact structure cbis shows a shock metamorphism and we report on several mineralogical and magnetic features pyrrhotite shows strong brittle deformation with a high density of stacking faults twinning parallel to the hexagonal 001 planes and average fault distances in the order of 10 nm although the determination of a superstructure was not possible due to the lattice defects the reflections of the nias subcell which is typical of all pyrrhotite modifications were clearly detected this phase is ferrimagnetic with a curie temperature tc between 350 and 365 c and suevite with this phase does not show the 34 k transition the most peculiar feature is the low metal sulfur ratio of 0 81 which indicates a distinctly higher vacancy concentration than for 4c pyrrhotite and a composition close to smythite fe9s11 this phase carries a stable natural remanent magnetization and is relatively hard magnetic steep inclinations of the natural remanent magnetization vector however suggest that this phase has been remagnetized by the drilling process a possible explanation is the magnetic domain size of faultless areas of about 10 nm in diameter which is at the lower limit of the single domain size near the threshold below which superparamagnetic behavior occurs the low thermal stability of this phase excludes postshock heating above 300 c for the suevite of the cbis our results imply that the iron deficient pyrrhotite is produced by shock metamorphism although an iron loss due to shock has never been reported before for pyrrhotite

40ar 39ar geochronologic constraints on the timing of massive sulfide and vein type pb zn mineralization in the western meseta of morocco the meseta domain of morocco is located on the southern margin of the late paleozoic hercynian orogenic zone 40ar 39ar ages of igneous and hydrothermal minerals biotite and illite were analyzed from a representative massive sulfide deposit at hajar 1 5 mt zn 0 45 mt pb 0 11 mt cu and 900 t ag and a vein type deposit at tighza 1 0 mt pb 0 3 mt zn and 1 000 t ag in the western meseta a weighted mean age of hydrothermal biotite of the hajar deposit is 300 9 2 6 ma 2 uncertainty identical to a hydrothermal illite age of 305 4 4 8 ma these two ages are calculated from about 93 percent of the released 39ar another illite age calculated from 74 percent of the released 39ar 313 4 9 1 ma overlaps with or is slightly older than these concordant ages these 40ar 39ar results indicate that the biotite and illite alteration of the hajar deposit formed almost simultaneously at 304 to 300 ma this age range is younger than the visean age previously assumed on the basis of geologic setting these 40ar 39ar ages are interpreted as the age of hydrothermal activity subsequent to massive sulfide mineralization a magmatic intrusion beneath the deposit may have triggered this hydrothermal activity three 40ar 39ar weighted mean ages and one plateau age from the tighza deposit range from 280 6 to 267 7 ma igneous biotite of the kaolin granite and hydrothermal illite of the ighrem aouss and north veins in the deposit indicate ages of 280 6 5 5 ma 280 6 3 1 ma and 275 5 3 4 ma respectively these three ages are identical within 2 uncertainties the age of the hydrothermal biotite from the mispickel granite 267 7 2 3 ma is slightly younger this younger age may have resulted from two periods of magmatic hydrothermal activity or from resetting of hydrothermal biotite by ar loss regardless these ages indicate that granite intrusion and hydrothermal alteration associated with galena and sphalerite bearing veins occurred mainly at 280 to 275 ma in the tighza deposit the identical ages of the magmatic intrusion and hydrothermal alteration suggest that the vein type pb zn mineralization as well as w mineralization was associated with the magmatic intrusion the influence of the late deformation and metamorphic overprint may be related to the lowest temperature steps of the analytical data the dates obtained from the lowest temperature steps from both the tighza and hajar deposits concentrate between 235 ma and 220 ma this time range is compatible with the geologic constraints on the deformation and these dates are thus attributed to the post visean regional metamorphism

comment on the paper by ch marignac sphalerite stars in chalcopyrite are they always the result of an unmixing process mineral deposita 24 176 182 1989

phase equilibria in the kfes 2 fe s system at 300 600 c and bartonite stability the article deals with phase relations in the kfes2 fe s system studied by the dry synthesis method in the range of 300 600 c and at a pressure of 1 bar at the temperature below 513 3 c pyrite coexists with rasvumite and there are pyrite rasvumite kfes2 and pyrite rasvumite pyrrhotite equilibria established above 513 3 c pyrite and rasvumite react to form kfes2 and pyrrhotite limiting the pyrite rasvumite association to temperatures below this in nature the experiments also outline the compositional stability range of the copper free analog of murunskite k x fe2 ys2 and suggest that mineral called bartonite is not stable in the cl free system at least at atmospheric pressure and the temperature in the experiments chlorbartonite could be easily produced after adding kcl in the experiment possible parageneses in the quaternary k fe s cl system were described based on the data obtained in this research and found in the previous studies the factors affecting the formation of potassium iron sulfides in nature were discussed

revisiting the field geology of taurus littrow abstract integration of apollo 17 field observations and photographs sample investigations lunar reconnaissance orbiter camera images chandrayaan 1 moon mineralogy mapper m3 spectra and miniature radio frequency mini rf s band radar images provides new insights into the geology of the valley of taurus littrow on the moon connecting the various remote observations to sample data enables a set of new conclusions to be drawn regarding the geological evolution of the valley structural considerations and published and recalculated 40ar 39ar analyses of samples from the north massif and the sculptured hills indicate that the crisium basin formed about 3 93 ga the serenitatis basin about 3 82 ga and the imbrium basin no earlier than 3 82 ga and no later than the average of 3 72 ga for 33 age dates from samples of the valley s mare basalts strong evidence continues to support the conclusion of others lucchitta 1972 spudis et al 2011 fassett et al 2012 that the sculptured hills physiographic unit consists of imbrium ejecta interpretation of m3 spectral data and apollo 17 samples indicate that rock units of the sculptured hills consist of a largely coherent mg suite pluton lroc nac stereo images and mini rf data indicate the presence of several exposed pyroclastic fissures across the sculptured hills rim boulders at camelot crater constitute nearly in situ wall rocks of that crater rather than ejecta and provide an opportunity for investigations of remanent magnetic field orientation at the time of the eruption of late mare basalt lavas in the valley paleomagnetic field orientation information also may be obtained relative to melt breccia contacts in north massif boulders that suggest original horizontal orientations lroc images indicate the existence of two temporally separate light mantle avalanche deposits the origin potential flow mechanisms and geology of the youngest avalanche from the south massif have been clarified the existence of two distinct light mantle avalanches raises doubt about the association of either light mantle avalanche with secondary impacts related to the tycho impact event alternatively the lee lincoln thrust fault appears to have triggered the second light mantle avalanche between 70 and 110 ma a simple structural analysis shows that this thrust fault dips 20 25 to the southwest where it crosses the north massif and to the west where it crosses the valley floor mini rf data reveal a line of reduced reflections roughly perpendicular to contours on the north massif about 3 km to the east of the lee lincoln fault although this line is possibly an older ancillary fault lroc nac stereo images indicate that it may be best explained as a pyroclastic fissure a debris flow of dark apparent pyroclastic ash lies below the southeast end of the potential fissure finally young lunar impact glass sample 70019 has been precisely located within lroc nac images and oriented for the first time using 60 mm f l sample documentation photographs sample 70019 can now be employed in lunar paleomagnetic field orientation studies

growth of large sulfide structures on the endeavour segment of the juan de fuca ridge abstract mapping and sampling with dsrv alvin has established that sulfide blocks 0 5 m across dredged from the axial valley of the endeavour segment at 47 57 n are samples of unusually large sulfide structures the steep sided structures up to 30 m in length 20 m in height and 10 15 m across are localized by venting along normal faults at the base of the western axial valley wall and are distributed for about 200 m along strike paralleling the 020 trend of the ridge crest high temperature fluids 350 to more than 400 c pass through the massive sulfide structures and enter seawater through small concentric nozzle like features projecting from the top or the sides of the larger vent structures diffuse low temperature flow is pervasive in the vicinity of the active sulfide structures exiting from basalt and sulfide surfaces alike evidence of recent volcanic activity is sparse the two largest samples taken with the dredge would not have been recoverable using the submersible these samples represent massive complex portions of the sulfide structures which were not closely associated with rapid high temperature fluid flow at the time of sampling they contain textural evidence of sealed hydrothermal fluid exit channels mineralogy is dominated by fe sulfides nnd amorphous silica pyrite marcasite wurtzite chalcopyrite and iss are the most common sulfide phases pyrrhotite galena and sphalerite are present in trace amounts barite amorphous silica and chalcedony are the only non sulfide phases anhydrite is not observed in any of the dredge samples although it is common in the chimney like samples recovered by alvin specific mineralogical textural zones within the dredge samples are anaoogous to individual layers in east pacific rise at 21 n and southern juan de fuca ridge samples with two exceptions a coarse grained highly porous fe sulfide rich interior containing sulfidized tubeworm casts and a 2 5 cm thick zone near the outer margin of the samples dominated by late stage amorphous silica the porous interior may have formed by dendritic crystal growth from a slowly circulating fluid within a large enclosed chamber the amorphous silica deposited from a seawater hydrothermal fluid mixture percolating slowly through the walls of the enclosed chamber conductive cooling of the fluid as it traversed the walls allowed amorphous silica to precipitate these silica rich zones are the densest most durable portions of the structures and may be responsible for the lasting stability of the large sulfide features observations in these samples are consistent with two distinct phases of development phase 1 is analogous to chimney growth and construction at 21 n and ends when flow channels become sealed to rapid flow of through going fluid the flow is evidently redirected within the structure phase 2 includes dissolution of anhydrite and precipitation of amorphous silica during conductive cooling of sluggishly circulating hydrothermal fluid or seawater hydrothermal fluid mixtures evolution of vent structures through phase 2 allows lateral and vertical growth of unusually large structures

magnetic characterization of non ideal single domain monoclinic pyrrhotite and its demagnetization under hydrostatic pressure up to 2 gpa with implications for impact demagnetization here we present a comprehensive magnetic characterization of synthesized non ideal single domain sd monoclinic pyrrhotite fe 7 s 8 the samples were in the form of a powder and a powder dispersed in epoxy non ideal refers to a powder fraction of predominantly sd size with a minor contribution of small pseudo single domain grains such non ideal sd pyrrhotite was found to be a remanence carrier in several types of meteorites carbonaceous chondrites snc which justifies the usage of synthetic compositions as analogous to natural samples data were collected from 5 to 633 k and include low field magnetic susceptibility 0 thermomagnetic curves major hysteresis loops back field remanence demagnetization curves first order reversal curves forcs alternating field and pressure demagnetization of saturation isothermal remanent magnetization sirm low temperature data such as zero field cooled and field cooled remanence datasets together with room temperature sirm cooling warming cycles as well as xrd and mossbauer spectra the characteristic besnus transition is observed at 33 k forc diagrams indicate interacting sd grains the application of hydrostatic pressure up to 2 gpa using nonmagnetic high pressure cells resulted in the demagnetization of the sample by 32 38 repeated cycling from 1 8 gpa to atmospheric pressure and back resulted in a total remanence decrease of 44 after 3 cycles pressure demagnetization experiments have important implications for meteorite paleomagnetism and suggest that some published paleointensities of meteorites with non ideal sd monoclinic pyrrhotite as remanence carrier may be lower limits because shock demagnetization was not accounted for

magnetic anisotropy behaviour of pyrrhotite as determined by low and high field experiments summary here we report on the sources of magnetic anisotropy in pyrrhotite an iron sulphide present in many rocks as an important carrier of the natural remanent magnetization while the magnetic hysteresis parameters of pyrrhotite are well known the existing database concerning its anisotropy behaviour is patchy and ambiguous therefore a collection of 11 seemingly single crystals of natural pyrrhotite was scrutinized before embarking on the anisotropy determinations the set of single crystals was extensively characterized rock magnetically by measuring curie temperatures hysteresis loops irm acquisition curves and forc diagrams the latter three all at room temperature first the variation of the low field susceptibility as function of applied field and grain size was evaluated for fields ranging from 1 to 450 a m 1 existing grain size dependent data and the present larger crystals show a logarithmic grain size dependence this enables estimating the grain size for unimodal pyrrhotite distributions in rocks measured trends are better fitted with an exponential function than with a rayleigh law style function based on the rock magnetic characterization and the behaviour of the anisotropy of magnetic susceptibility six samples of the original 11 were selected for the high field anisotropy determinations within the basal plane those data were acquired with a torque cantilever type magnetometer as expected most single crystals showed a pure 6 curve within their basal plane because of the easy axis configuration in some crystals however lower harmonic terms overlapped the 6 term this may be the dominant source of the observed variation in magnetic anisotropy properties torque data of three of the six samples were of sufficient quality to allow evaluation of k 1 re evaluation of existing torque data and including the present newly derived determinations yields for the anisotropy constant of pyrrhotite within the basal plane k 1 2 7 0 2 10 4 jm 3 this is over an order of magnitude more precise than the sparse existing k 1 data only the value reported by mikami and co authors in 1959 agrees with the new determination with this firmly established k 1 value meaningful anisotropy models are now possible for pyrrhotite bearing rocks

phase relations involving pyrrhotite below 350 degrees c a hydrothermal recrystallization method was employed to determine the phase relations in the fe s system involving pyrrhotite between 350 degrees and 115 degrees c the superstructures of pyrrhotite as designated by nakazawa and morimoto 1970 1971 are considered to be thermodynamic phases the solvus between pyrite and hexagonal 1c 1 pyrrhotite continues below 325 degrees c along the slope established by toulmin and barton 1964 to 308 degrees c where a discontinuity marks the upper stability of the mc superstructure the solvus then continues along a similar slope to 262 degrees c where with the onset of the na superstructure there is a discontinuity and the curve reverses slope sharply at 254 degrees c monoclinic 4c pyrrhotite becomes stable in the peritectoid reaction hexagonal na pyrrhotite 47 30 at fe pyrite monoclinic 4c pyrrhotite 47 25 at fe monoclinic pyrrhotite exists over a range of compositions the maximum being 46 4 to 46 9 at percent fe at 115 degrees c hexagonal pyrrhotite is separated from monoclinic pyrrhotite by a narrow miscibility gap down to the upper stability limit of the nc superstructure at 209 degrees c below 209 degrees c the miscibility gap widens with hexagonal nc pyrrhotite of 47 3 at percent fe coexisting with monoclinic pyrrhotite of 46 9 at percent fe at the sulfur rich limit of the stability field monoclinic pyrrhotite coexists with pyrite the phases greigite smythite and marcasite were not encountered our results are in reasonable agreement with those obtained previously by hydrothermal synthesis methods but they are in disagreement with some results obtained in dry experiments which have produced metastable phase assemblages the phase diagram is compatible with natural pyrrhotite occurrences and in particular with those from geothermal boreholes at broadlands new zealand from which samples were recovered at known quench temperatures on the other hand our studies cast considerable doubt on the validity of the pyrrhotite geothermometer as applied to ores

mineralogy parageneses and phase relations of copper iron sulfides in the atlantis ii deep red sea new investigations are carried out on the mineralogy and mineral chemistry of sulfide assemblages obtained in samples from one core in the hydrothermally active southwest basin of the atlantis ii deep red sea the most abundant sulfide phases are the exsolved intermediate solid solution iss and chalcopyrite sphalerite pyrrhotite marcasite mackinawite and presumably wurtzite are also observed two distinct groups of paragenesis were encountered a intermediate solid solution with sphalerite incrustations and intergrowths and b intermediate solid solution barren of sphalerite intergrowths the first group is confined to the upper part of the co zone and the soan zone backer and richter 1973 and the second is present in the entire core 100 3 7 an optically isotropic chalcopyrite is found for the first time as a natural mineral in atlantis ii red sea yet its existence as a novel phase needs x ray confirmation it exhibits a lower reflectivity than normal chalcopyrite and is isotropic chalcopyrite occurs either as a single phase or in association with tetragonal chalcopyrite our investigations indicate that the formation of atlantis ii deposits is a result of complex processes these processes are characterized by compositional changes in the ore bearing fluids and the change in sulfur fugacity especially with depth the presence of exsolved chalcopyrite lamellae in iss indicates slow cooling below 450 c however it is difficult to understand why the cubic chalcopyrite is not converted to the tetragonal form even though the temperature of transformation lies above 450 c 470 500 c cabri 1973 the cu fe ratio changes in the exsolved chalcopyrite lamellae from core to rim of the composite grains the ratio is higher in the rims this suggests that primary inhomogenous iss grains formed from solutions with a continuous increase in the cu fe ratio slow cooling is also required to account for the exsolution of chalcopyrite lamellae in iss the low sulfur content in isotropic chalcopyrite is also suggestive of low fs2 the low s content in the chalcopyrite may be the controlling factor for the sluggish conversion from cubic to tetragonal chalcopyrite mackinawite lamellae show the same orientation in iss and exsolved isotropic chalcopyrite indicating that mackinawite exsolved before the breakdown of iss this strongly suggests that mackinawite is stable above 300 c contrary to experimental results by zoka et al 1973 pyrrhotite was probably formed by the sulfurization of ilvaite the pyrrhotite grains with several complex successive zones show the sequence of the sulfurization episodes

analysis of pyrrhotite properties accompanying recrystallization of metamorphosed nickel sulfide ore from kambalda western australia serial sectioning was carried out on a single sample of oriented pyrrhotite pentlandite ore from the durkin shoot at kambalda this permitted the sequential investigation of a number of pyrrhotite properties including grain morphologies triple junction angles grain lattice orientation microhardness peak broadening in x ray diffractograms and approximate fe s ratios of the monoclinic pyrrhotite by microprobe analysis the present study confirms the presence of previously identified flattened tabular f and equant polyhedral e pyrrhotite morphologies and establishes that the e type has recrystallized from the f variety the latter is composed of subgrain aggregates with c axes that tend to be oriented perpendicular to the pyrrhotite foliation formation of the e type pyrrhotite from the f variety involved subgrain rotations subgrain coalescence and grain growth this was accompanied by definite reductions in values for triple junction angles and in microhardness as well as apparent reductions i

oxide sulphide relationships in sodalite bearing metasomatites of the epembe swartbooisdrif alkaline province north west namibia the south eastern part of kunene intrusive complex kic namibia angola is host to volumetrically significant and economically important concentrations of sodalite in the area around swartbooisdrif north west namibia the mineralisation was formed by metasomatic exchange with carbonatites of the epembe swartbooisdrif alkaline province this process led to the breakdown of ore minerals initially present in various rock types of the kic and caused the formation of new opaque phases in the sodalite bearing metasomatites a detailed investigation of textures and chemical compositions of the fe ti oxides and sulphides has allowed evaluation of the complex ore forming processes related to the polyphase magmatic and metasomatic history of the sodalite deposit the predominant opaque phases in the various rock types of the kic are ilmenite and titano magnetite which are highly concentrated in the so called magnetite plugs it is clear from the textural evidence that most of the ilmenite and titano magnetite although of orthomagmatic origin recrystallised under subsolidus conditions conformably their respective chemical compositions and phase relations represented in the system feo 1 2fe2o3 tio2 point to re equilibration at temperatures below 600 c ilmenite and titano magnetite were affected by later deformation and decomposed by various reactions related to or outlasting the metasomatic process oxidation of ilmenite led to the formation of symplectitic aggregates of rutile and secondary magnetite carbonatisation of the fe ti oxides produced rutile and the siderite and rhodochrosite components in ankerite pyrite in part together with rutile and secondary magnetite was formed by sulphidation of the fe ti oxides conspicuous aggregates of granular or lamellar intergrowths of pyrite with hematite and or magnetite are interpreted as products of contemporaneous sulphidation and oxidation of former igneous pyrrhotite rarely observed pyrrhotite with pentlandite lamellae is probably not an igneous relic but was formed during the metasomatic event smaller amounts of chalcopyrite bornite digenite chalcocite galena ferroan siegenite millerite and polydymite testify to different cooling stages during or after metasomatism applying the phase relations in the simplified system fe co ni s o we were able to reconstruct a semi quantitative t f s2 f o2 path for the ore forming processes

pyrrhotite varieties from the 9 1 km deep borehole of the ktb project we used transmission electron microscopy tem to study pyrrhotite from the german continental deep drilling kontinentale tiefbohrung ktb project our goals were to determine the distribution of structure types with depth and to establish relationships between the bulk thermomagnetic behavior and the microstructures of pyrrhotite in samples from the deep section of the borehole 9080 m below surface which is equivalent to an in situ temperature of similar to 260 degrees c the dominant variety of pyrrhotite is 1c that has a mostly disordered vacancy distribution faint diffuse superstructure reflections in the selected area electron diffraction saed patterns indicate some nc like ordering occurs probably in small domains in addition to the disordered pyrrhotite a 5c type is also present according to bulk thermomagnetic measurements pyrrhotite grains from 9080 m are antiferromagnetic at room temperature we attribute this behavior to the dominance of the disordered 1c type in the upper section of the hole at 564 and 2325 m several pyrrhotite varieties occur but the 4c type is most common in agreement with the ferrimagnetic character of most pyrrhotite grains optical microscopy of pyrrhotite grains that are covered with a magnetic colloid reveal intergrown ferrimagnetic and antiferromagnetic lamellae tem images show that these grains are intergrowths of 4c 5c and nc types we interpret these microstructural variations to be responsible for the variation in magnetic properties within single pyrrhotite grains

sulfide composition and phase relations in the fe ni cu ore deposits of the ivrea verbano basic complex western alps italy the bulk composition mineralogy and mineral chemistry of base metal sulfides have been investigated in the fe ni cu ore deposits of the ivrea verbano basic complex

ore mineralogy of the applachian caledonian stratabound sulfide deposits abstract the diverse ore mineralogies of more than 100 stratabound sulfide deposits that occur along the length of the appalachian caledonian orogen have been tabulated the minerals reflect the varying cu zn pb ratios that have been used as a means to separate the ore deposits into six distinct types following the igcp project 60 guidelines the ore deposits each containing at least one million metric tons of ore are typical of massive sulfide deposits throughout the world and provide a basis for contrasting and comparing this orogen with others differing grades of metamorphism have significantly modified the ore mineral grain sizes and textures but do not seem to have effectively influenced the number or variety of mineral species present

mineralogy of iron sulfides in cm1 and ci1 lithologies of the kaidun breccia records of extreme to intense hydrothermal alteration the polymict kaidun microbreccia contains lithologies of c type chondrites with euhedral iron sulfide crystals of hydrothermal origin our fib tem study reveals that acicular sulfides in a cm1 lithology are composed of fe rich pyrrhotite with nonintegral vacancy superstructures nc pyrrhotite troilite and pentlandite all showing distinct exsolution textures based on phase relations in the fe ni s system we constrain the temperature of formation of the originally homogeneous monosulfide solid solution to the range of 100 300 c in some crystals the exsolution of pentlandite and the microtextural equilibration was incomplete probably due to rapid cooling we use thermodynamic modeling to constrain the physicochemical conditions of the extreme hydrothermal alteration in this lithology unless the cm1 lithology was sourced from a large depth in the parent body internal pressure 85 bar or the temperatures were in the lower range of the interval determined the water was likely present as vapor previously described light 34s compositions of sulfides in kaidun s cm1 lithology are likely due to the loss of 34s enriched h2s during boiling platy sulfide crystals in an adjacent intensely altered ci1 lithology are composed of fe poor monoclinic 4c pyrrhotite and nc pyrrhotite and probably formed at lower temperatures and higher fs2 relative to the cm1 lithology however a better understanding of the stability of fe poor pyrrhotites at temperatures below 300 c is required to better constrain these conditions

sulfide mineralogy and redox conditions in some shergottites magmatic sulfide mineralogy has been studied in 2 olivine phyric shergottites dag 476 and sau 005 and 4 basaltic shergottites zagami shergotty los angeles and nwa 480 modal abundances of magmatic sulfides as estimated by image analysis on thin section are high 0 16 to 0 53 area percent and correlate positively with abundances of fe ti oxides sulfides are mesostasis minerals being mostly interstitial grains or locally enclosed in post cumulus melt inclusions e g sau 005 in olivine sulfides in shergottites are composed of major pyrrhotite containing pentlandite exsolutions associated with minor amounts of cu sulfides chalcopyrite and or cubanite hot desert finds e g dag 476 show abundant fracture filling iron oxy hydroxides of probable terrestrial origin unaltered sulfides show metal rich hexagonal pyrrhotite compositions with metal sulfur m s ratio ranging between 0 936 0 005 and 0 962 0 01 this compositional range corresponds to the two phase structural domain 2c nc of the fe s system however the high temperature disordered hexagonal 1c pyrrhotite structure would be in better agreement with magnetic properties of shergottites ni contents in pyrrhotite increase from los angeles 0 05 at to shergotty zagami and nwa 480 0 2 0 5 at and dag 476 and sau 005 up to 3 at the higher ni values of pyrrhotite in olivine phyric shergottites correlate with the abundance of pentlandite exsolutions both reflecting more primitive ni rich sulfide liquids where abundant olivine crystallized this result and the strong correlation between sulfide abundances and fe ti oxides argue for a primary magmatic origin of these sulfides although they reproduce the trend of magmatic oxygen fugacity conditions determined from fe ti oxide pairs observed pyrrhotite compositions are systematically more metaldeficient compared to those calculated from the fe s o system this suggests post magmatic oxidation during cooling on mars followed by terrestrial weathering for hot desert finds

mineralogy and magnetic behavior of pyrrhotite from a 260 c section at the ktb drilling site germany the ultradeep bore hole of the german continental deep drilling program ktb reached a depth of 9100 m and in situ temperatures of about 260 c offering an unique opportunity to study natural pyrrhotite an integrative approach using optical methods electron microprobe analysis x ray diffraction transmission electron microscopy see posfai et al 2000 and temperature dependent magnetic susceptibility measurements were used to characterize pyrrhotite types as a function of lithology and depth we found a lithology controlled distribution of pyrrhotite types to a depth of 8080 m with ferrimagnetic monoclinic 4c pyrrhotite metal content 46 0 to 47 2 at as the dominant magnetic phase in gneisses and metabasic rocks in the gneisses a second pyrrhotite type with higher metal concentrations 46 9 to 48 2 at and antiferromagnetic behavior also occurs at depths greater than 8080 m in situ temperature 230 c antiferromagnetic pyrrhotite predominates in all lithologies that 4c pyrrhotite does not occur below 8080 m suggests that 4c is unstable above 230 c in these rocks instead of 4c a 5c type with a ferrimagnetic structure occurs below 8080 m thermomagnetic experiments indicate that the metal poor weiss type pyrrhotite is stabilized by oxygen that causes the formation of magnetite during heating from our observations on natural pyrrhotites we suggest that the magnetic transition is related to the growth of ordered na pyrrhotite domains to single domain size

copper gold and silver enrichment in ore mylonites within massive sulphide orebodies at hongtoushan vhms deposit n e china abstract the hongtoushan archaean cu zn volcanic hosted massive sulphide vhms deposit occurs in the hunbei granite greenstone terrane liaoning province of ne china the ores were metamorphosed 3 0 2 8 ga to upper amphibolite facies at temperatures between 600 and 650 c and underwent three phases of deformation the deformation has transposed the stratiform orebodies into a y shaped configuration ore minerals in the deposit were originally composed of pyrite pyrrhotite chalcopyrite and sphalerite prograde metamorphism obliterated almost all the sedimentary textures in the ores and the present ore textures were formed substantially during peak and post peak metamorphism intensive remobilisations have occurred in the hongtoushan deposit at various scales there are more than 30 oreshoots inside the main massive sulphide orebodies the oreshoots range from 2 to 30 m in length 0 1 to 1 5 m in width and 2 to 30 m in depth extension most run parallel or sub parallel to the strike of the massive sulphide ore layers with only a few being developed in metamorphic rocks in the immediate vicinity of the sulphide orebodies almost all the sulphide and gangue minerals in the oreshoots have been affected by intense shearing pyrite is characterised by cataclastic flow pyrrhotite chalcopyrite and sphalerite exhibit strong plasticity hydrothermal alteration minerals in the oreshoots are dominated by deformation free hornblende actinolite epidote clinozoisite biotite muscovite albite carbonate and quartz cu au and ag in the ore mylonites average 11 wt 1 74 and 235 g t respectively compared to the massive sulphide ores these oreshoots show remarkable enrichment of these elements with enrichment coefficients of 5 3 5 0 and 4 6 respectively we draw the conclusion that these oreshoots are actually ore mylonites overprinted by late stage fluids the presence of annealing textures in pyrrhotite and the absence in pyrite suggest that formation and succeeding annealing of the ore mylonite took place over the temperature range from 550 to 450 c such a temperature range combined with the geology and mineralogy indicates that these ore mylonites and the derivative oreshoots were formed during upper greenschist facies retrograde metamorphism similarity of the ore mylonites to the massive ores in metal varieties and lead isotope ages suggest that cu au and ag of the overprinting fluids on the ore mylonites were derived mainly from the nearby massive sulphide ores however lead isotope compositions of the ore mylonites also suggest that an external source such as the metamorphic host rocks has also contributed to their metal budget

distribution of chalcophile and platinum group elements among pyrrhotite pentlandite chalcopyrite and cubanite from the noril sk talnakh ores implications for the formation of platinum group minerals in most magmatic sulfide deposits platinum group elements pge are found both within the structure of the base metal sulfides bms pyrrhotite po pentlandite pn chalcopyrite ccp and cubanite cbn and as platinum group minerals pgm tellurium as bi sb and sn tabs are essential elements in many of these pgm the potential role of tabs in collecting pge and thus forming a pge deposit has not been closely investigated we have determined the concentrations of a full suite of chalcophile elements in po pn ccp and cbn using laser ablation inductively coupled plasma mass spectrometry on samples from the noril sk talnakh ni deposits in these deposits the po rich ore is thought to represent monosulfide solid solution mss cumulate of the initial sulfide liquid and the ccp rich ore a mixture of the fractionated sulfide liquid and intermediate solid solution iss the bms from the po rich ore contain lower concentrations of tabs pd pt and au and higher concentrations of mo ru rh re os and ir than bms from the ccp rich ores this observation is consistent with experimental results which show that tabs pd pt and au are incompatible with mss whereas the other elements are compatible in mss counter intuitively in the po rich ore the bulk of the pd and tabs is hosted by bms this is because during crystallization although only a small amount of the incompatible elements partitioned into the bms the fractionated liquid has migrated away thus the po rich ores represent mss adcumulates therefore as the po rich ores contain very little trapped liquid fraction the bms host the bulk of pd and tabs in contrast in the ccp rich ore the bulk of au pd pt and tabs is present as pgm or electrum grains this is because more trapped liquid is present and as tabs au pd and pt are not compatible with iss they concentrated into the very last sulfide liquid and crystallized as intergrowths of pd pt tabs pgm the tabs then do not appear to collect pd pt and au but rather all elements are concentrated in the most fractionated sulfide liquid by crystal fractionation

mid proterozoic ferruginous conditions reflect postdepositional processes to evaluate the mechanics of mid proterozoic environmental iron transport and deposition we coupled microscale textural and bulk rock magnetic techniques to study the 1 4 ga lower belt group belt supergroup montana and idaho we identified a pyrrhotite siderite isograd that marks metamorphic iron bearing mineral reactions beginning in subgreenschist facies samples even in the best preserved parts of the basin secondary overprints were common including recrystallization of iron bearing sulfides base metal sulfides and nanophase pyrrhotite despite these overprints a record of redox chemistry was preserved in the early diagenetic framboidal pyrite and detrital iron oxides including trace nanoscale magnetite that remained after sulfidization in anoxic and sulfidic sedimentary pore fluids based on these results we interpret the belt basin as having oxic waters at least in shallow water environments with no indication of abundant ferrous iron in the water column this is consistent with the cooccurrence of early eukaryotic fossils within the same strata

integrating long offset transient electromagnetics lotem with seismics in an exploration environment1 the applications of electromagnetics have increased in the past two decades because of an improved understanding of the methods improved service availability and the increased focus of exploration in the more complex reservoir characterization issues for electromagnetic methods surface applications for hydrocarbon exploration and production are still a special case while applications in borehole and airborne research and for engineering and environmental objectives are routine in the past electromagnetic techniques in particular deep transient electromagnetics made up a completely different discipline in geophysics although many of the principles are similar to the seismic one with an understanding of the specific problems related to data processing initially and then acquisition the inclusion of principles learned from seismics happened almost naturally initially the data processing was very similar to seismic full waveform processing the hardware was also changed to include multichannel acquisition systems and the field procedures became very similar to seismic surveying as a consequence the integration and synergism of the interpretation process is becoming almost automatic the long offset transient electromagnetic lotem technique will be summarized from the viewpoint of its similarity to seismics the complete concept of the method will also be reviewed an interpretation case history that integrates seismic and lotem from a hydrocarbon area in china clearly demonstrates the limitations and benefits of the method