formation of large sulfide mineral deposits along fast spreading ridges example from off axial deposits at 12 43 n on the east pacific rise abstract submersible investigations with nautile near the 13 n hydrothermal field on the epr were made in 1992 we selected diving areas based on deep towed side scan sonar imaging close to a pit crater at the top of a young seamount 2 km east of the axial ridge we discovered one of the largest 70 m high and 200 m in diameter sulfide mounds formed at a fast spreading ridge 12 cm yr despite an overlap in composition between axial and off axial deposits the general trend reflects real differences in compositions off axis deposit differs from axial deposits by the scarcity of zinc sulfides and cobalt and selenium enrichment sulfur isotope variation is minimal for the off axis seamounts and suggests that sulfides precipitated from unmodifed end member hydrothermal solutions axial sulfides have a broader range due to reduction of seawater sulfate at mixing fronts between hydrothermal and seawater solutions along the axial graben fault system lead isotopic compositions of sulfides are in two overlapping but distinct fields indicating different pb sources and separate convective systems for the seamount and the axial deposits our observations suggest that the plumbing system is stable and centred on a shallow localised magma chamber under the seamount this configuration is by far more efficient than unstable axial processes to create during several hydrothermal episodes major sulfide deposits near a fast spreading ridge off axis seamounts are localised areas with high magmatic budget able to drive and focus hydrothermal systems at the same place for a long time other known occurrences of sulfides related to seamounts are at less than 11 km from the ridge axis thus we suggest that off axial volcanoes close to the ridge are first order targets to discover active or inactive large deposits along fast to medium spreading ridges

lewis ponds a hybrid carbonate and volcanic hosted polymetallic massive sulphide deposit new south wales australia the lewis ponds zn pb cu ag au deposit located in the eastern lachlan fold belt central western new south wales exhibits the characteristics of both volcanic hosted massive sulphide and carbonate hosted replacement deposits two stratabound massive to disseminated sulphide zones main and toms occur in a tightly folded upper silurian sequence of marine felsic volcanic and sedimentary rocks they have a combined indicated resource of 5 7 mt grading 3 5 zn 2 0 pb 0 19 cu 97 g t ag and 1 9 g t au main zone is hosted by a thick unit of poorly sorted mixed provenance breccia limestone clast breccia and quartz crystal rich sandstone whereas toms zone occurs in the overlying siltstone pretectonic carbonate chalcopyrite pyrite and quartz pyrite stringer veins occur in the footwall porphyritic dacite south of toms zone strongly sheared dolomite chalcopyrite pyrrhotite veins directly underlie the toms massive sulphide lens the mineralized zones consist predominantly of pyrite sphalerite and galena paragenetically early framboidal dendritic and botryoidal pyrite aggregates and tabular pyrrhotite pseudomorphs of sulphate occur throughout the breccia and sandstone beds that host main zone but are rarely preserved in the annealed massive sulphide in toms zone main and toms zones are associated with a semi conformable hydrothermal alteration envelope characterized by texturally destructive chlorite dolomite and quartz rich assemblages dolomite chlorite quartz calcite and sulphides have selectively replaced breccia and sandstone beds in the main zone host sequence whereas the underlying porphyritic dacite is weakly sericite altered vuggy and botryoidal textures resulted from partial dissolution of the dolomite altered sedimentary rocks and unimpeded growth of base metal sulphides carbonate and quartz into open cavities the intense chlorite rich alteration assemblage underlying toms zone grades outward into a weak pervasive sericite quartz assemblage with distance from the massive sulphide lens limestone clasts and hydrothermal dolomite at lewis ponds are enriched in light carbon and oxygen isotopes the dolomite yielded 13cvpdb values of 11 to 1 and 18ovsmow values of 6 to 16 liquid vapour fluid inclusions in the dolomite have low salinities 1 4 7 7 equiv wt nacl and homogenization temperatures 166 232 c for 1 000 m water depth dolomitization probably involved fluid mixing or fluid rock interactions between evolved heated seawater and the limestone bearing facies prior to and during mineralization 34svcdt values range from 2 0 to 5 0 in the massive sulphide and 3 9 to 7 4 in the footwall carbonate chalcopyrite pyrite stringer veins indicating that the hydrothermal fluid may have contained mamgatic sulphur and a component of partially reduced seawater the sulphide mineral assemblages at lewis ponds are consistent with moderate to strongly reduced conditions during diagenesis and mineralization low temperature dolomitization of limestone bearing facies in the main zone host sequence created secondary porosity and provided a reactive host for fluid rock interactions main zone formed by lateral fluid flow and sub seafloor replacement of the poorly sorted breccia and sandstone beds base metal sulphide deposition probably resulted from dissolution of dolomite fluid mixing and increased fluid ph pyrite sphalerite and galena precipitated from a relatively low temperature 150 250 c hydrothermal fluid in contrast toms zone was emplaced into fine grained sediment at or near the seafloor above a zone of focused up flowing hydrothermal fluids copper rich assemblages were deposited in the toms zone footwall and massive sulphide lenses in main and toms zones as the hydrothermal system intensified during the d1 deformation fracture controlled fluids within the lewis ponds fault zone and adjacent footwall volcanic succession remobilized sulphides into syntectonic quartz veins lewis ponds is a rare example of a synvolcanic sub seafloor hydrothermal system developed within fossiliferous limestone bearing facies the close spatial association between limestone hydrothermal dolomite massive sulphide and dacite provides a basis for new exploration targets elsewhere in new south wales

controls on the siting and style of volcanogenic massive sulphide deposits abstract volcanogenic massive sulphide vms deposits form in subaqueous environments from circulating hydrothermal fluids heated by volcanic activity these deposits form as sulphide mounds stratiform exhalative and or replacive bodies and commonly have stockwork vein mineralization in their immediate footwall these various styles are essentially facies of mineralization each one being the product of a particular set of conditions that control the ore forming processes and the consequent geometry and architecture style of the deposits these controls include the physical and or chemical nature of the host rocks the temperature and composition of the hydrothermal fluids and the redox state of the depositional environment the style of exhalative deposits is controlled by the salinity of the vented fluids and the redox state at the seafloor hydrothermal fluids with salinities less than twice that of seawater that vented into open oxic oceanic environments typically formed small mound and chimney complexes unless they were rapidly covered by sediments or volcanic rocks the massive sulphides were rapidly oxidized and partly dissolved by seawater in contrast stratiform sheet like deposits are typically formed in anoxic bottom waters anoxic marine conditions were periodically of global extent particularly prior to 2 4 ga or of a regional nature local anoxic conditions can also be self induced by the exhalation of saline and reducing hydrothermal fluids that ponded in bathymetric depressions such as second or third order basins to form a brine pool these exhalative systems may have been initiated as chimney vent complexes and subsequently overlain by stratiform sulphides formed under the self induced anoxic conditions deposits formed in anoxic environments can be significantly larger than those in oxic settings and this is attributed to several factors that include longer lived hydrothermal circulation more efficient sulphide precipitation and reduced or inhibited oxidation thereof replacement of volcanic and sedimentary strata by sulphide typically occurs within the feeder zones beneath the exhalative mineralization however successions with abundant porous permeable and or reactive rocks such as glassy and or pumiceous volcaniclastic rocks and in some cases limestone favoured the development of large replacive deposits that may have had little surficial expression on the sea floor vms deposits at spreading centres within oceanic crust formed almost exclusively as mounds most of them have not been preserved likely due to oxidation of the sulphides in the prevailing oxic environment and or destruction of oceanic crust during subsequent subduction intra continental rifts arc rifts and back arc rifts commonly have more complexity in their structure and facies architecture and environments and can host all styles of vms mineralization in these settings early extension favoured the formation of restricted basins with ideal conditions for the onset of hydrothermal activity and development of anoxic bottom waters whereas in mature rifts the conditions were less conducive for the formation of regionally extensive anoxic environments formation of replacive deposits was permissible in all settings with porous or reactive subsea floor strata replacive mineralization is the most likely to be preserved in the geological record due to the sulphides being physically shielded from oxidative weathering and mechanical erosion at the seafloor the various styles of vms mineralization can rarely be distinguished using a single criterion in most cases multiple criteria are required mound style mineralization is distinguished by a mound or lens shaped morphology b presence of chimney fragments c presence of abundant sedimented sulphide breccias d location on a stratigraphic boundary ore horizon and e association with a thin horizon or thicker stratigraphic interval of fine grained clastic rocks e g shale mudstone that accumulated at slow sedimentation rates stratiform exhalative mineralization is distinguished by a sheet like morphology prior to deformation b presence of fine grained clastic host rocks that accumulated at relatively slow rates e g mudstone c presence of local or extensive planar stratification replacive mineralization is characterized by a irregular geometry and distribution of sulphide bodies b gradation from massive sulphides to semi massive sulphides and disseminated mineralization with relict textures of the host rock and c originally pumiceous glassy or reactive host rocks emplaced at high depositional rates mass flow deposits lavas carbonate altered mass flow deposits or limestone one deposit or district may comprise two or more of these main styles of mineralization in many cases the main styles of vms mineralization present in a particular region can be predicted from examination of the facies architecture and depositional environments of the host succession recognition of the style s of mineralization that occur in a particular basin or mineral belt enables exploration models to be improved and should influence the strategy of exploration for vms deposits

heat and salt fluxes in the atlantis ii deep red sea abstract the atlantis ii deep is located on the red sea axial rift it is a topographic depression enclosing a volume of about 17 km3 between 1 900 m and 2 200 m depth that contains layered brines of temperatures up to 66 c and salinities up to 270 previous geochemical investigations showed that the hot brines result from discharge of hydrothermal solutions that have exchanged heat and chemical components with the basaltic substratum the last investigation of the deep in 1992 showed that the brines occurred in four well mixed layers with the shallowest at a depth of 2 000 m the temperature and salinity profiles describe a transition zone from 2 000 m to 1 900 m above which red sea water occurs the distribution of temperature and salt in this transition zone appears to be controlled by the topography of the deep the hydrographic structure of the brine column has been documented in the literature for seven time intervals between 1966 and 1992 examination of these data shows that the system changed with time the evolution of the entire package of brines that fill the deep shows the following changes 1 the temperature of the brines increased 2 the salinity of the solutions increased 3 the two brine layers described in 1966 still existed in 1992 but new layers appeared above them 4 for 26 years almost all additional heat and salt supplied in the deep were confined to the depression and were not dispersed into the overlying seawater the fourth point indicates that a heat and salt balance for the deep can be calculated the calculation of the heat that entered into the system was divided into two components the temperature increase of the brines and the heat loss at the wall rock the latter component was negligible the rate of heat input to the deep was constant during the period considered and amounted to 0 54 109 w the salt input was also constant and equalled 250 350 kg s during the period 1966 1992 heat and salt were most probably supplied by a hydrothermal solution with an average range of flow rate temperature and salinity of 670 1000 kg s 195 310 c and 270 370 respectively

the abundance of seafloor massive sulfide deposits the possibility of mining seafl oor massive sulfide deposits has stirred debate about the sustainable use of this new resource and whether commercial development is worth the risk among the outstanding questions is how many deposits might be accessible to deep sea mining more than 300 sites of high temperature hydrothermal venting have been identifi ed since the discovery of black smokers but signifi cant massive sulfide accumulation has been found at only 165 of these sites estimates of the total number of vent fields and associated mineral deposits based on plume studies and deposit occurrence models range from 500 to 5000 we have used new deposit occurrence data from 10 000 km of ridge arc and backarc spreading centers to estimate the amount of massive sulfide in the easily accessible neovolcanic zones of the global oceans the total accumulation in these areas is estimated to be on the order of 6 108 tonnes containing 3 107 tonnes of copper and zinc this is similar to the total discovered copper and zinc in cenozoic massive sulfi de deposits mined on land but is insuffi cient to satisfy a growing global demand for these metals

chemical processes in buoyant hydrothermal plumes on the east pacific rise near 21 n hydrothermal plume water containing suspended particles of precipitated black smoke has been sampled from three hydrothermal vent fields on the east pacific rise near 21 n the samples were taken within the lower 22 m of the buoyant plumes directly above 273 350 c black smoker vents using go flo bottles mounted on the submersible alvin based on li as a conservative tracer of the high temperature endmember solution mixing ratios of 102 to 104 g seawater g vent water are achieved within the lower 22 m of the plumes the particle concentrations sampled in the lower 13 m of the plumes are much larger than predicted for these mixing ratios suggesting that the particles are settling within the lower part of the plume the major minerals in the smoke are pyrrhotite fe rich sphalerite pyrite unidentified fe s si and fe si s phases chalcopyrite amorphous silica sulfur fe oxyhydroxides including goethite and anhydrite present in trace quantities are barite isocubanite wurtzite covellite marcasite and unidentified silicates and alsilicates organic matter is common the composition of the plume solutions indicates that 35 25 of the hydrothermally injected fe remains in dissolved form i e 0 45 m within the lower 22 m of the plume in spite of a 3 to 9 fold excess of h2s in the vent solutions nearly all of the mn and si and most of the ba also remain in solution h2s by contrast has been largely 70 100 removed by precipitation as sulfides and sulfur but mainly by oxidation to dissolved species with intermediate oxidation states its early removal implies that 50 30 of the injected fe will eventually precipitate as primary oxides rather than as sulfides and that fe can be fractionated from the other chalcophile metals during sulfide precipitation compared with the vent water the particles are enriched in cu co ag cd al zn pb and ni by factors of 4 to 20 relative to fe and depleted in ba s si and mn scavenging from seawater may play a role in co and cu enrichment at the ngs field and for ag cd and ni at all three fields but is negligible for pb and zn these results indicate that two distinct metalliferous components are delivered to the distal regions of a plume as a result of reactions in the lower part of the buoyant plume 1 1 a dissolved component that includes about half the fe and all of the mn and will eventually precipitate as oxides and 2 2 a particulate component consisting of fine grained sulfide minerals that are enriched in ore metals by factors of 4 to 20

geochemical and sedimentological considerations of a permanently anoxic fjord framvaren south norway abstract framvaren a fjord in south norway is an example of extreme anoxia due to the geomorphological features sill depth 2 m basin depth 180 m the postglacial history of framvaren is outlined emphasizing the preservation of environmental changes in the properties of the water and the sediments high levels of hydrogen sulfide in the water 170 180 ml l 1 or 7 8 mm h 2 s dense populations of photosynthetic bacteria at the redox boundary total number 3 10 6 ml 1 metal sulfide formation in the anoxic water e g framboidal pyrite and zinc sulfide and organic rich bottom sediments with high metal content e g 1000 ppm zn are typical examples the rate of sedimentation is estimated in three independent ways suggesting an average annual flux of 100 g m 2 yr 1 in the central basin of framvaren fluxes of organic matter and zinc to the sediments are calculated and compared with potential sources

facies analyses and volcanic setting of the giant neves corvo massive sulfide deposit iberian pyrite belt portugal in the iberian pyrite belt volcanic rocks are relatively scarce accounting for approximately only 25 of the geologic record with the remaining 75 consisting of sedimentary units this association is very clear in the host succession to the neves corvo massive sulfide deposit in portugal the neves corvo host succession comprises the products of explosive and effusive rhyolitic eruptions intercalated with mudstone that records a submarine below wave base environment and provides precise biostratigraphic age constraints the first and second volcanic events involved eruptions at local intrabasinal vents the first event generated thick beds of fiamme breccia that are late famennian in age the fiamme were originally pumice clasts produced by explosive eruptions and were subsequently compacted the second event was the late strunian latest famennian effusion of rhyolitic lava that was pervasively quench fragmented the third and final event is younger than the massive sulfide deposits poorly represented in the mine area and minor compared with the two other events the integration of biostratigraphic data with the volcanic facies architecture indicates that the neves corvo ore deposits are similar in age to the late strunian rhyolitic lava although regionally the iberian pyrite belt is essentially a sedimentary succession ore formation at neves corvo can be closely linked to discrete volcanic events that produced a relatively narrow range of volcanic facies

active and relict sea floor hydrothermal mineralization at the tag hydrothermal field mid atlantic ridge the tag hydrothermal field is a site of major active and inactive volcanic hosted hydrothermal mineralization in the rift valley of the slow spreading mid atlantic ridge at 26 degree n the axial high is the principal locus of present magmatic intrusions the tag field contains three main areas of present and past hydrothermal activity 1 an actively venting high temperature sulfide mound 2 two former high temperature vent areas 3 a zone of low temperature venting and precipitation of fe and mn oxide deposits the volcanic centers occur at the intersections between ridge axis parallel normal faults and projected axis transverse transfer faults the intersections of these active fault systems may act as conduits both for magmatic intrusions from sources beneath the axial high that build the volcanic centers and for hydrothermal upwelling that taps the heat sources radiometric dating of sulfide samples and manganese crusts in the hydrothermal zones and dating of sediments intercalated with pillow lava flows in the volcanic center adjacent to the active sulfide mound indicate multiple episodes of hydrothermal activity throughout the field driven by heat supplied by episodic intrusions over a period of at least 140 times 10 sup 3 yr the sulfide deposits are built by juxtaposition and superposition during relatively long residence times near episodic axial heat sources counterbalanced by mass wasting in the tectonically active rift valley of the slow spreading oceanic ridge hydrothermal reworking of a relict hydrothermal zone by high temperature hydrothermal episodes has recrystallized sulfides and concentrated the first visible primary gold reported in a deposit at an oceanic ridge

hydrothermal fluids associated with seafloor mineralization at two southern kermadec arc volcanoes offshore new zealand massive sulfide samples have been recovered from brothers and rumble ii west volcanoes of the southern kermadec frontal arc northeast of new zealand both are caldera forming volcanoes with brothers largely dacitic and rumble ii west basaltic to basaltic andesite in composition the sulfide samples are considered to be pieces of chimneys from near the base of the caldera walls and are dominated by cu fe ba pb chalcopyrite pyrite barite galena and to a lesser extent zn fe ba pb sphalerite pyrite barite galena mineralization gold is present in the samples up to 6 1 ppm paragenetic relationships suggest that the two hydrothermal systems have heated up and later cooled down oxidation of the sulfides is common and suggests that parts of the deposits are relatively old fluid inclusion microthermometric data show salinities fall predominantly in the range 3 0 to 3 4 wt nacl equivalent similar to seawater values 3 2 wt about 15 of the brothers salinity data range to both lower 2 2 wt and higher 3 9 wt than seawater values homogenization temperatures for type i inclusions in barite range between 175 and 322 c for the brothers samples and between 205 and 268 c for one rumble ii west sample a dramatic decrease in temperature and or change in the oxidation state of the hydrothermal fluid are considered the main mechanisms responsible for gold deposition at the kermadec vent sites this was achieved by mixing the hydrothermal fluid with ambient seawater within what are inferred to have been 300 c white smoker chimneys consistent with s isotope results fluid inclusion volatiles are dominated by h2o 99 81 99 98 mol followed by co2 0 03 0 17 and lesser amounts of n2 0 004 0 023 ch4 0 002 0 026 and trace cos and c2 c3 hydrocarbons fluid inclusions hosted by barite contain noticeably lesser amounts of gas than those within sulfides consistent with mixing the source of the relatively high concentrations of ch4 is enigmatic although may be related to the thermal degradation of organic rich sediments intercalated within the volcanic pile addition of a pressure correction and the effect of dissolved gases show that the hydrothermal fluids did not boil at the chimney depths however the range of measured salinities in the brothers field combined with slightly positive trends in fluid inclusion co2 ch4 versus co2 n2 plots suggest sub seafloor phase separation may have occurred in the hydrothermal system prior to venting

relationships between kuroko volcanogenic massive sulfide vms deposits felsic volcanism and island arc development in the northeast honshu arc japan the northeast ne honshu arc was formed by three major volcano tectonic events resulting from late cenozoic orogenic movement continental margin volcanism before 21 ma seafloor basaltic lava flows and subsequent bimodal volcanism accompanied by back arc rifting 21 to 14 ma and felsic volcanism related to island arc uplift 12 to 2 ma eight petrotectonic domains parallel to the ne honshu arc were formed as a result of the eastward migration of volcanic activity with time major kuroko volcanogenic massive sulfide vms deposits are located within the eastern marginal rift zone kuroko rift that formed in the final period of back arc rifting 16 to 14 ma volcanic activity in the ne honshu arc is divided into six volcanic stages the eruption volumes of volcanic rocks have gradually decreased from 4 600 km3 per 1 my for a 200 km long section along the arc of basaltic lava flows in the back arc spreading stage to 1 000 2 000 km3 of bimodal hyaloclastites in the back arc rift stage and about 200 km3 of felsic pumice eruptions in the island arc stage the kuroko vms deposits were formed at the time of abrupt decrease in the eruption volume and change in the mode of occurrence of the volcanic rocks during the final period of back arc rifting in the area of the kuroko rift felsic volcanism changed from aphyric or weakly plagioclase phyric before 14 ma to quartz and plagioclase phyric with minor clinopyroxene 12 to 8 ma to hornblende phyric after 8 ma and hornblende and biotite phyric after 4 ma the kuroko vms deposits are closely related to the aphyric rhyolitic activity before 14 ma the rhyolite was generated at a relatively high temperature from a highly differentiated part of felsic magma seated at a relatively great depth and contains higher nb ce and y contents than the post kuroko felsic volcanism the kuroko vms deposits were formed within a specific tectonic setting at a specific period and associated with a particular volcanism of the arc evolution process therefore detailed study of the evolutional process from rift opening to island arc tectonics is very important for the exploration of kuroko type vms deposits

foliation boudinage control on the formation of the rosebery pbzn orebody tasmania abstract the rosebery pb zn ag au massive sulphide deposit occurs within the middle cambrian mount read volcanics of western tasmania it is hosted by a tuffaceous slate lens that is surrounded by felsic volcanics the volcanic belt and its ordovician cover were deformed and metamorphosed during an early to middle devonian orogeny tabberabberan orogeny during this orogeny d 3 e w shortening was partially accommodated by reverse bedding parallel shearing within the slate unit and immediately underlying volcanic rocks this caused reactivation and intensification of an early foliation s 2 and the development of asymmetric chocolate tablet foliation boudinage structures with boudin necks parallel to the x and y directions the mineralization occurs along extensional shear planes that are associated with foliation boudinage mineralogical zoning in the orebody can be directly related to dilational bends in shears associated with foliation boudin necks it is proposed that these structures gaped during the d 3 deformation allowing infiltration of metalliferous hydrothermal fluids along shear plane and cleavage directions into the fractured wall rock progressive metasomatic replacement of the wall rock resulted in the formation of a sulphide sulphate silicate orebody the orebody is completely discordant to folds in the host rock this observation confirms a structurally controlled origin and refutes earlier interpretations of the deposit as a tightly folded chemical sediment isotope data indicate that the orebody was probaby derived from volcanogenic sulphides within the mount read volcanics the rosebery orebody is best regarded as a metamorphogenic deposit that formed by dissolution upward transport concentration and re precipitation of primary sulphides the proposed macroscopic model complements separate microstructural evidence by the author indicating a syn d 3 timing of mineralization

shale basins sulfur deficient ore brines and the formation of exhalative base metal deposits abstract the massive sulfide deposits of the iberian pyrite belt are interbedded with felsic volcanic rocks and shale and underlain by several thousand meters of siliciclastic sedimentary rocks known as the pq group isotope geochemistry and regional geology are both consistent with equilibration of the ore forming fluids with the pq group prior to ore deposition near the former seafloor the average cu zn pb ratio of the pq group rocks ca 26 55 19 is similar to the weighted average of all the massive sulfide orebodies combined ca 25 52 23 the genetic relationship between massive sulfide deposits and a siliciclastic sedimentary metal source is explained here by a thermodynamic model proposing that mildly reducing redox conditions imposed by equilibration with the sedimentary rocks are most critical for the formation of an effective ore forming fluid relatively metal rich but organic poor pyrite bearing shale undergoing dewatering of saline pore fluids is an effective source for the generation of sulfur deficient but relatively iron and base metal rich brines thus we propose that the giant deposits of the iberian pyrite belt owe their existence not to exceptionally metal enriched e g magmatic fluids but to the existence of a fairly ordinary but large metal source in reactive siliciclastic sediments combined with an underlying igneous heat source and a particularly efficient mechanism of sulfide precipitation by mixing with h 2 s rich fluids at or near the seafloor essentially similar mineral equilibria are imposed when saline fluids are buffered by typical continental basement rocks leaching of retrograde minerals and possibly residual salts from their magmatic or metamorphic prehistory is expected to generate similar variably metal rich but relatively sulfide deficient fluids thus the existence of mildly reducing rocks can be the dominant chemical control in the source of fluids generating many volcanogenic irish type or sedex deposits many of which are known to precipitate their metal load in response to biogenic sulfide addition at the ore deposition site

flow rates in the axial hot springs of the east pacific rise 21 n implications for the heat budget and the formation of massive sulfide deposits abstract the first in situ measurements of flow rates in submarine hot springs temperatures between 275 and 350 c were made in the hot springs of the east pacific rise at 21 n during november 1981 the flow rates ranged between 0 7 and 2 4 m s we estimate that the total rates at which heat and mass are transported from the three hot spring areas obs national geographic and southwest vents are ca 2 2 108 w and 150 kg of fluid s respectively the very high rate of heat loss precludes the existence of hot springs as steady state features of the east pacific rise at 21 n we estimate that hot springs are active for a maximum of ca 40 000 years chemical and or mechanical clogging of the vents can drastically reduce the lifetime of the hot springs using a simple model of plume development 1 we calculated that less than 3 of the sulfide particles that are entrained in the hydrothermal plumes at 21 n settle from the plumes before dispersal by a lateral submarine current at a height of ca 250 m above the seafloor 2 the time that is required to form the sulfide mounds that surround the hot springs by the accumulation of sulfide particles that settle from the plumes is ca 70 85 years the current rate at which sulfide particles settle from the hydrothermal plumes and accumulate near the hot springs appears to be too small to lead to the formation of large massive sulfide deposits such as the mavrouni deposit on cyprus 3 within the time limits that are suggested by our thermal energy balance calculations

carbon and oxygen isotope halo in carbonates related to the mcarthur river hyc zn pb ag deposit north australia implications for sedimentation ore genesis and mineral exploration a study of carbon and oxygen isotope ratios in fine grained sedimentary dolomite in the barney creek formation of the mcarthur basin demonstrates the presence of an extensive isotope halo surrounding the giant stratiform hyc zn pb ag deposit dolomite within the halo shows an 18o enriched and 13c depleted isotope signature 18o 23 to 26 smow 13c 2 to 3 5 pdb relative to normal proterozoic sedimentary dolomite beyond the halo 18o 20 23 and 13c 0 to 2 the c o isotope halo within the dolomitic siltstones extends at least 15 km southwest of the hyc deposit and approximately coincides with a previously defined lithogeochemical halo of elevated fe mn zn pb and tl dolomitic siltstone lamellae within the stratiform zn pb ag ores at hyc exhibit an isotopic range similar to that of the halo dolomites suggesting that the ore and halo equilibrated with the same hydrothermal fluid modeling of isotopic exchange accompanying fluid rock interaction suggests that the halo dolomites equilibrated with low temperature fluids 50 120 c which were enriched in 18o 18o 5 5 but with an average crustal carbon isotope signature 13c 6 1 our preferred interpretation is that the oxygen and carbon isotope halo at hyc is related to the development of an extensive brine pool this pool was deepest in the vicinity of the hyc deposit adjacent to the emu fault and it became shallower to the southwest away from the fault using the carbon isotope fractionation equation between dolomite and hc batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document o 3 mbox end document it is possible to estimate the temperature variation at the base of the brine pool during the accumulation of the barney creek formation brine pool temperatures were highest in and adjacent to the hyc deposit 40 70 c and decreased to values of 17 to 30 c remote from the deposit these temperatures are similar to those recorded in the red sea brine pool associated with the atlantis ii metalliferous sediment deposit based on our work at hyc and lady loretta strata bound 18o enriched carbonate lithogeochemical halos may be a characteristic of the proterozoic stratiform zn pb ag deposits of northern australia these halos are more extensive than the narrow 18o depletion halos recorded in dolomites surrounding skarn mississippi valley type and irish style zn pb deposits this fundamental difference in the isotopic halo characteristics of these groups of zinc deposits is probably related to the low temperature synsedimentary brine pool origin of the north australian sedex deposits in contrast to the various replacement and open space fill origins of skarn mississippi valley type and irish style deposits

radiochronological investigation of hydrothermal deposits from the meso zone central indian ridge abstract hydrothermal activity in the indian ocean has hitherto only been poorly documented first indications of hydrothermal mineralization were observed in 1987 during the gemino cruise over the 4th ridge segment of the central indian ridge 270 km north of the rodriguez triple junction subsequent cruises in 1993 hydrotrunc and in 1995 hydrock were carried out in order to obtain detailed information about the geological setting and the extent and mineral distribution of the field but primarily to sample the first massive sulfides of the indian ocean floor this hydrothermal field which was called the meso zone was studied by detailed mapping and by ocean bottom photography hydrothermal precipitates were recovered with a tv grab sampler at four sampling locations two in the northern part of the mineralized field called the talus tips site and two in the central part called the sonne field the sulfide samples were age dated using the 230 th 234 u method they show different periods of activity at each site 52 5 22 7 3 and 16 2 ka for the main events at the talus tips site and 18 2 and 12 5 1 5 ka for the sonne field we conclude from these data that the two sites were not active at the same time if it is assumed that there is a complete cessation of activity between 52 and 23 ka for more recent periods from 23 to 10 ka it may be postulated that the deep seated hydrothermal circulation is continuous but that the discharge of hot fluid occurs alternately at the sonne field or at the talus tips site comparing our results with those obtained previously at the different hydrothermal sites we favor the conclusion of episodic activity moreover in the sonne field jasper formation resulting from a low temperature hydrothermal event dated at around 11 ka is presently the youngest hydrothermal formation in the entire meso zone

evolution and source of ore fluids in the stringer system hellyer vhms deposit tasmania australia evidence from fluid inclusion microthermometry and geochemistry the hellyer deposit is a classic large tonnage high grade mound style volcanic hosted massive sulphide vhms deposit in the cambrian mt read volcanic belt of western tasmania in the footwall directly underlying the deposit there is an extensively altered pipe which cootains a well developed and preserved stringer zone the vein paragenesis at hellyer indicates that premineralization stage i veins consist entirely of quartz and occur throughout the alteration pipe the synmineralization stage 2 veins are the most abundant veins in the stringer zone and consist of three sub stages stage 2a veins of crustiform quartz pyrite and carbonate with minor amounts of chalcopyrite sphalerite and galena stage 2b veins with abundant base metal sulphides minor quartz carbonate and barite gangue and stage 2c veins of coarsely crystalline barite with variable amounts of pyrite sphalerite galena and carbonate stages 3 6 veins are postmineralization veins and are related to the devonian tabberabberan orogeny textural petrographic and microthermometric investigations of fluid inclusions in the hellyer stringer system indicate that type i primary liquid vapour inclusions occur along growth planes of crustiform quartz crystals or within colour banding of zoned sphalerite these inclusions are 10 15 m in size and yielded homnogenisation temperatures of 170 220 c in early 2a veins 165 322 c in main stage 2b veins and 190 256 c io late stage 2c veins these data suggest a waxing and waning thermal history however the average salinity remained between 8 11 naci equiv wt in all stage 2 veins chalcopyrite bearing primary fluid inclusions have been recognised in the base metal rich stage 28 veins no evidence for presence of co2 e g formation of clathrates was recorded by rnicrothermometry however laser raman spectroscopic lrs analysis indicates the presence of co2 1 mole in the stage 2b veins and no detectable co2 in 2a and 2c vein stages semi quantitative sem wds microprobe analyses of fluid inclusion decrepitates indicate that the hellyer ore fluid was enriched in potassium and calcium but depleted in magnesium relative to seawater pixe microanalysis of fluid inclusions in quartz indicates that the stage 2b ore fluids have a significantly higher base metal concentration compared to the stage 2a veins the postmineralization stage 4 veins have a variable but lower base metal content in this study there was no fluid inclusion evidence of boiling cation composition higher salinities relative to seawater and the presence of co2 suggest that recycled seawater alone cannot be the sole source of the ore fluids this interpretation is in agreement with previous isotopic studies in the hellyer stringer system although direct input of bulk ore constituents from a magma chamber cannot be demonstrated from the present fluid inclusion data such a contribution of ore fluids from a magmatic source cannot be ruled out the possible input from the magmatic source may have occurred during the base metal rich stage 2b vein formation characterised by the intensifying temperature of deposition higher base metals and co2 contents

composition and dissolution of black smoker particulates from active vents on the juan de fuca ridge during two atlantis ii alvin cruises to the juan de fuca ridge in 1984 active high temperature 140 284 c vents were sampled for black smoker particulates using the grassle pump individual mineral phases were identified using standard x ray diffraction and petrographic procedures in addition elemental compositions and particle morphologies were determined by x ray energy spectrometry and scanning electron microscope x ray energy spectrometry techniques the vent particulates from the southern juan de fuca ridge vent sites were highly enriched in s si fe zn and cu and were primarily composed of sphalerite wurtzite pyrite pyrrhotite barite chalcopyrite cubanite hydrous iron oxides and elemental sulfur two additional unidentified phases which were prevalent in the samples included an fe si phase and a ca si phase the grain sizes of the individual particle phases ranged from 100 m for the fe si particles grain size and current meter data were used in a deposition model of individual phase dispersal for many of the larger sulfide and sulfate particles the model predicts dispersal to occur over length scales of only several hundreds of meters the high temperature black smokers from the more northerly endeavour segment vents were highly enriched in fe s ca cu and zn and were primarily composed of anhydrite chalcopyrite sphalerite barite sulfur pyrite and other less abundant metal sulfide minerals the grain sizes of the individual particles ranged from 10 m to slightly larger than 500 m the composition and size distributions of the mineral phases are highly suggestive of high temperature mixing between vent fluids and seawater a series of field and laboratory studies were conducted to determine the rates of dissolution of several sulfate and sulfide minerals the dissolution rates ranged over more than 3 orders of magnitude from 3 2 10 8 cm s 1 for anhydrite to 1 2 10 12 cm s 1 for chalcopyrite the results indicate that for some minerals particularly anhydrite and marcasite total dissolution occurs within a few hours to a few weeks of their formation for other more stable minerals including pyrite sphalerite and chalcopyrite the time required for total dissolution is much longer and consequently individual crystals may be expected to persist in the sediments for considerable periods of time after deposition

the internal structure of an active sea floor massive sulphide deposit the hydrothermal circulation of sea water through permeable ocean crust results in rock water interactions that lead to the formation of massive sulphide deposits these are the modern analogues of many ancient ophiolite hosted deposits1 4 such as those exposed in cyprus here we report results obtained from drilling a series of holes into an actively forming sulphide deposit on the mid atlantic ridge a complex assemblage of sulphide anhydrite silica breccias provides striking evidence that such hydrothermal mounds do not grow simply by the accumulation of sulphides on the sea floor indeed the deposit grows largely as an in situ breccia pile as successive episodes of hydrothermal activity each form new hydrothermal precipitates and cement earlier deposits during inactive periods the collapse of sulphide chimneys dissolution of anhydrite and disruption by faulting cause brecciation of the deposit the abundance of anhydrite beneath the present region of focused hydrothermal venting reflects the high temperatures 150 c currently maintained within the mound and implies substantial entrainment of cold sea water into the interior of the deposit these observations demonstrate the important role of anhydrite in the growth of massive sulphide deposits despite its absence in those preserved on land

types of massive sulphide deposits in the urals massive sulphide deposits in the urals are found within volcanic and volcanic sedimentary sequences of ordovician to middle devonian ages four types of economic sulphide deposits have been recognized cyprus besshi urals and baimak the cyprus type copper sulphide deposits are hosted by mafic volcanites that occur in the basal parts of palaeozoic volcanic sequences the besshi type copper zinc deposits are located within clastic sedimentary rocks intercalated with basalts and andesites zinc copper deposits of the urals type are hosted by bimodal rhyolite basalt assemblages which occur at a higher stratigraphic level than those of cyprus and besshi types the baimak type zinc copper barite deposits are associated with intrusive quartz porphyries which occur in the upper parts of bimodal volcanic successions in addition there are some sulphide deposits of zinc lead barite and zinc copper composition hosted by ordovician terrigenous sequences which occur within depressions in precambrian blocks these types of sulphide deposits have been formed at various stages of divergence and convergence of the earth s crust during the orogenic history of the urals

trace metal distribution in the atlantis ii deep red sea sediments the atlantis ii deep is one of the only locations on the modern seafloor where active formation of a brine pool type stratiform ore deposit can be studied the presence of the brine pool causes retention of the hydrothermally released metals within the brine covered area resulting in the accumulation of 90 mt of low grade metalliferous sediment 2 06 zn 0 46 cu 41 g t ag and 0 5 g t au guney et al 1988 almost all metals are derived from hydrothermal input but some are also derived from seawater e g mo pelagic phytoplankton ni and detrital input cr the hydrothermal fluid that is vented into the pool is rich in metals but relatively low in reduced sulfur compared to open ocean black smokers metals are deposited as sulfides from the cooling hydrothermal fluid but also by adsorption onto non sulfidic surface active particles si fe ooh in the brine pool an unexpected increase in the cu zn ratio of the sediments with distance from the vent source s may reflect pulses of higher temperature venting and increased cu fluxes to the brine pool which are recorded as higher cu zn ratios in the distal sediments or alternatively more efficient adsorption of cu to fe ooh particles in the distal brine during early diagenesis a few thousand years metals that are loosely bound to surface active particles in the sediment apparently react with h2s to form sulfides proximal to the inferred vents the ambient pore water is highly concentrated in trace metals such as cd ag and hg that are incorporated in diagenetic sulfides including chalcopyrite and sphalerite at greater distance from the vents trace metals such as mo as and ga are taken up by framboidal pyrite high concentrations of au up to 3 ppm are found in both proximal and distal metalliferous sediments indicating that both primary deposition with sulfides and adsorption by diagenetic pyrite are important depositional processes some of the inferred pathways for metal precipitation in the atlantis ii deep sediments especially adsorption onto surface active particles and subsequent incorporation in sulfides during diagenesis may have been important unrecognized processes for metal accumulation in ancient stratiform ore deposits thought to have formed in brine pools

initiation and organizational modes of an extreme rain producing mesoscale convective system along a mei yu front in east china abstractthe initiation and organization of a quasi linear extreme rain producing mesoscale convective system mcs along a mei yu front in east china during the midnight to morning hours of 8 july 2007 are studied using high resolution surface observations and radar reflectivity and a 24 h convection permitting simulation with the nested grid spacing of 1 11 km both the observations and the simulation reveal that the quasi linear mcs forms through continuous convective initiation and organization into west east oriented rainbands with life spans of about 4 10 h and their subsequent southeastward propagation results show that the early convective initiation at the western end of the mcs results from moist southwesterly monsoonal flows ascending cold domes left behind by convective activity that develops during the previous afternoon to evening hours suggesting a possible linkage between the early morning and late afternoon peaks of the mei yu rainfall two scales of convective organization are found d

4 transpressional tectonics lower crust decoupling and intrusion of deep mafic sills a model for the unusual metallogenesis of sw iberia abstract sw iberia is interpreted as an accretionary magmatic belt resulting from the collision between the south portuguese zone and the autochthonous iberian terrane in variscan times 350 to 330 ma in the south portuguese zone pull apart basins were filled with a thick sequence of siliciclastic sediments and bimodal volcanic rocks that host the giant massive sulphides of the iberian pyrite belt massive sulphides precipitated in highly efficient geochemical traps where metal rich but sulphur depleted fluids of dominant basinal derivation mixed with sulphide rich modified seawater massive sulphides formed either in porous reactive volcanic rocks by sub seafloor replacement or in dark shale by replacement of mud or by exhalation within confined basins with high biogenic activity crustal thinning and magma intrusion were responsible for thermal maturation and dehydration of sedimentary rocks while magmatic fluids probably had a minor influence on the observed geochemical signatures the ossa morena zone was a coeval calc alkaline magmatic arc it was the site for unusual mineralization particularly magmatic ni cu and hydrothermal fe oxide cu au ores iocg most magmatism and mineralization took place at local extensional zones along first order strike slip faults and thrusts the source of magmas and iocg and ni cu deposits probably lay in a large mafic ultramafic layered complex intruded along a detachment at the boundary between the upper and lower crust here juvenile melts extensively interacted with low grade metamorphic rocks inducing widespread anatexis magma contamination and further exsolution of hydrothermal fluids hypersaline fluids 18 o fluid 5 4 to 12 were focused upward into thrusts and faults leading to early magnetite mineralization associated with a high temperature 500 c albite actinolite salite alteration and subsequent copper gold bearing vein mineralization at somewhat lower temperatures assimilation of sediments by magmas led in turn to the formation of immiscible sulphide and silicate melts that accumulated in the footwall of the layered igneous complex further injection of both basic and sulphide rich magmas into the upper crust led to the formation of ni cu rich breccia pipes younger 330 to 280 ma peraluminous granitoids probably reflect the slow ascent of relatively dry and viscous magmas formed by contact anatexis these granitoids have w sn and pb zn related mineralization that also shows geochemical evidence of major mantle crust interaction late epithermal hg cu sb and pb zn ag mineralization was driven by convective hydrothermal cells resulting from the high geothermal gradients that were set up in the zone by intrusion of the layered igneous complex in all cases most of the sulphur seems to have been derived from leaching of the host sedimentary rocks 34 s 7 to 20 with only limited mixing with sulphur of magmatic derivation the metallogenic characteristics of the two terranes are quite different in the ossa morena zone juvenile magmatism played a major role as the source of metals and controlled the styles of mineralization in the south portuguese zone magmas only acted as heat sources but seem to have had no major influence as sources of metals and fluids which are dominated by crustal signatures most of the magmatic and tectonic features related to the variscan subduction and collision seem to be masked by those resulting from transpressional deformation and deep mafic intrusion which led to the development of a metallogenic belt with little resemblance to other accretionary magmatic arcs

origin of the eskay creek precious metal rich volcanogenic massive sulfide deposit fluid inclusion and stable isotope evidence the eskay creek deposit is an unusual polymetallic au ag rich volcanogenic sulfide sulfosalt deposit located in the iskut river area of northwestern british columbia canada economic concentrations of precious and base metals are contained in the 21 zone which is divided into a number of subzones as of december 31 1998 total production and proven probable reserves are 1 9 million tons mt at 60 2 g t au 2 652 g t ag 3 2 percent pb 5 2 percent zn and 0 7 percent cu the 21b zone which contains the bulk of the reserves began production in 1995 the mineralization occurs mainly as well preserved stratiform clastic beds of sulfide sulfosalt debris and also as discordant footwall quartz sulfide veins the hydrothermal system that formed the eskay deposit was low temperature

australian volcanic hosted massive sulfide deposits features styles and genetic models the cambro ordovician period has yielded the major development of volcanic hosted massive sulfide vhms deposits in australia resulting in about 12 million metric tons of contained metal copper lead and zinc concentrated in the mount read volcanics tasmania and the mount windsor volcanics queensland the archean 4 million metric tons of metal and the silurian 3 5 million metric tons of metal constitute the next important episodes while the devonian and permian have produced isolated deposits the deposits range from cu type to zn cu type to zn pb cu type the zn cu type deposits are restricted to the archean and silurian whereas the cu type and zn pb cu type occur sporadically throughout the time span from early archean to permian in general terms the major vhms bearing districts are calc alkaline in character and display a thick basal pile of rhyolitic volcanics 1 3 km thick including lavas epiclastics and subvolcanic intrusions which is overlain by a polymodal sequence containing various proportions of rhyolite dacite andesite basalt and sediments the major deposits are commonly located at the top contact of the rhyolite pile or within the lower part of the overlying polymodal sequence there is a wide range in variability of styles of australian vhms deposits including mounds pipes sheets layered deposits stacked deposits stockwork and disseminated deposits distal reworked deposits and cyclic layered deposits although these various styles show a range of features there is a consistent theme across the spectrum of metal zonation alteration mineralogy alteration chemistry sulfur isotopes macrotextures microtextures and host volcanic relationships which strongly suggests that they all belong to the one genetic group of ore deposit the classic mound style deposits such as hellyer have a series of key features subsets of which are represented in the other deposit styles the mound deposits are considered to form from deposition of metal sulfides on the sea floor immediately around the hydrothermal vent growth of the mound occurs by upward replacement of sulfide assemblages stable at higher fluid temperatures leading to zone refining and lead zinc silver gold enrichment in the outer and upper parts of the mound departure from the classic mound style of deposit is related principally to three key factors the chemistry of the ore fluid salinity temperature f02 and ah2s the nature permeability and chemistry of the volcanic pile and the sea hoor environment sea hoor topography and seawater depth these factors control the aspect ratio of the deposit the extent of stringer zone development the degree of subsea floor replacement mineralization the nature and spatial development of footwall alteration and the development and style of related distal mineralization sulfur isotope studies of australian vhms deposits indicate that reduced seawater sulfate is a major source of sulfur in the deposit whereas lead and strontium isotope results are compatible with the metals being derived by seawater convection and leaching from the volcanic pile and basement rocks this conclusion is supported by the application of various leaching models which demonstrate the availability of an adequate source of both base and precious metals in the footwall volcanic sequences the input of metals directly from volcanic magma chambers is not precluded by the available data and one likely scenario involves the contribution of gold and copper from a magmatic vapor plume rising to mix with convective seawater fluids which contribute lead zinc silver and gold leached from the footwall volcanics and basement rocks the relative importance of the magmatic input compared with the seawater convective input may help to explain the spectrum of deposit styles arid their spatial relationship to volcanic centers or adjacent sedimentary basins

seafloor hydrothermal systems driven by the serpentinization of peridotite 1 heat balance models predict that heat released upon serpentinization of peridotites can result in a wide range of hydrothermal venting temperatures temperatures ranging from a few to a few tens of c are likely temperatures 300 c may be possible in conjunction with significant heat input from below low fluid flow rate 10 kg s a high rate of serpentinization 100 kg s or some combination of these factors the volume of fresh lithosphere accessible to serpentinization may limit the duration of an episode of hydrothermal venting when the serpentinization rate exceeds 10 kg s hydrothermal venting driven by high rates of serpentinization may occur episodically as new reaction surfaces are made available by tectonic activity or crack propagation given the uncertainty of several parameters the current episode of venting at the lost city vent field on the mid atlantic ridge may range from 102 to 104 years

mineralogy bulk and rare earth element geochemistry of massive sulphide associated hydrothermal sediments of the brunswick horizon bathurst mining camp new brunswick massive sulphides are spatially and temporally associated with iron formation if and other hydrothermal sedimentary rocks in the vicinity of the brunswick no 12 brunswick no 6 and austin brook deposits bathurst mining camp sulphide carbonate oxide and silicate predominant if is present carbonate predominant if is best developed in and around the brunswick no 12 deposit whereas hematite bearing if is absent here but prominent in the austin brook brunswick no 6 area the if is composed dominantly of si co2 fe mn and ca minor constituents include mg p ti al and s statistically significant interelement correlations between eu fe mn pb zn cd au ca sr ba p co2 and s indicate that these elements were precipitated from hydrothermal fluids vented onto the seafloor positive interelement correlations between si ti al mg k zr rare earth elements ree s except eu se v y yb co ni and cr reflect the presence of detrital clastic mafic and aluminosilicate minerals and

constraints on water depth of massive sulfide formation evidence from modern seafloor hydrothermal systems in arc related settings the results of three decades of seafloor research provide the most reliable information on the importance of water depth in massive sulfide formation available data from over 130 occurrences show that water depths of seafloor vent sites vary with plate tectonic setting and the regional magmatic and volcanic environment the shallowest hydrothermal systems in subduction related settings are hosted by arc volcanoes these shallow vent sites have a number of features in common with subaerial epithermal systems massive sulfide occurrences in arc related rifts the most likely setting for many ancient analogs are generally restricted to water depths from 700 to 2 000 m with rifts developing within old arc crust at the deeper end of this range back arc spreading centers proximal to arcs host massive sulfide deposits at depths of 1 500 to 2 000 m the deepest hydrothermal systems occur along mature back arc spreading centers distal to volcanic arcs where water depths range from 2 000 to 3 700 m these deeper vent sites probably represent the best modern analogues of ophiolite hosted massive sulfide deposits boiling of the hydrothermal fluids is common at volcanic arcs and in arc related rifts in these environments elevated magmatic gas contents of the hydrothermal fluids can contribute to the widespread occurrence of phase separation and associated gas loss by contrast the high ambient pressures in deep marine hydrothermal systems along mature back arc spreading centers prevent fluids from boiling during their ascent to the seafloor boiling controls the maximum temperature at which hydrothermal fluids discharge at the seafloor and therefore influences the metal content of seafloor sulfide deposits copper rich massive sulfides typically occur at water depths exceeding 1 000 m whereas zn and pb rich occurrences may form at any water depth boiling can be an important control on ag and au grades but is not the only factor controlling precious metal enrichment in massive sulfides shallow marine hot spring deposits can be highly enriched in trace metals such as as hg and sb submarine volcanic arc and back arc settings are geologically complex and significant variations in water depth can occur over short distances paleoenvironmental reconstruction of these environments in ancient volcanic terranes is hampered by the lack of unequivocal volcanological or sedimentological criteria that indicate water depth the relationships established here using modern seafloor observations provide important constraints on the paleoenvironmental setting of ancient volcanic hosted massive sulfide deposits

the subsea floor formation of volcanic hosted massive sulfide evidence from the ansil deposit rouyn noranda canada the ansil cu zn volcanic hosted massive sulfide deposit is located approximately 14 km north northwest of rouyn noranda quebec within the blake river group of the archean southern abitibi greenstone belt the deposit is the second lowest within the central mine sequence a series of bimodal rhyolite andesite formations that fill in the noranda cauldron host to 17 volcanic hosted massive sulfide deposits the deposit consists of a single massive sulfide lens situated at the contact between rhyolite of the northwest formation and overlying andesite of the rusty ridge formation the rhyolite flow forms a ridge up to 500 m high which was inundated by the andesite flows the orebody is hosted within a unit of quartz porphyritic finely layered felsic volcaniclastite cranston tuff that fills in an east west trending graben formed on the upper surface of the rhyolite flow at the east end of the graben the cranston tuff is interlayered with a thin unit of dacite flows the deposit lies within an extensive discordant alteration zone characterized by feldspar destruction and na depletion the zone extends from 400 m below the deposit at the contact of the synvolcanic flavrian intrusive complex to over 400 m above the deposit this alteration zone is controlled by a fault system that served as a focus for hydrothermal fluid upflow from the beginning of cauldron formation until the end of the first cauldron cycle within the na depletion zone there are three distinct alteration facies associated with the orebody early hydrothermal activity is defined by hydrothermal explosion breccias that formed along the base of the east west trending graben walls they were filled with finely banded quartz albite sphalerite pyrite and the wall rock altered to sericite quartz with finely disseminated sphalerite and pyrite pyrrhotite the graben was then filled with the cranston tuff which was selectively altered and mineralized by the zn rich fluid subsequent development of northerly trending faults was accompanied by the upflow of cu rich fluid that selectively chloritized the footwall rhyolite below the graben floor and formed a

formation of massive sulfide deposits on oceanic ridge crests incremental reaction models for mixing between hydrothermal solutions and seawater equilibrium path calculations have been used to model mixing between hot 350 c hydrothermal solutions and ambient seawater in an attempt to simulate mineral precipitation at seafloor vents these calculations predict temperatures of precipitation paragenetic sequence of minerals and chemical composition of chimney deposits associated with vents on the seafloor at 21 n epr assuming sulfate sulfide disequilibrium during mixing the paragenetic sequence revealed is chalcopyrite anhydrite pyrrhotite pyrite sphalerite graphite and barite when sulfate sulfide equilibria is permitted during mixing however reduction of small amounts of sulfate results in early precipitation of pyrite and a sequence of cu rich sulfide minerals chalcopyrite bornite chalcocite covellite this sequence is analogous to that observed in thin chimney walls the calculations indicate that sulfide mineral precipitation occurs in response to both cooling and change in composition of the hydrothermal solutions as a result of mixing varying the amount of mixing with respect to temperature simulating conductive heating of seawater prior to mixing results in only minor variations in the sequence and abundance of precipitated phases anhydrite precipitation during mixing occurs early which is consistent with formation of an anhydrite leading edge of chimney structures similarly extrapolation of warm spring data from galapagos to zero so4 concentration suggests anhydrite formation due to mixing with seawater beneath the seafloor most likely below the level of reactive calcareous sediments subsequent interaction of the mixed hydrothermal solution with those sediments results in elevated and variable ca concentrations estimated for end member solutions from the galapagos precipitation of mg hydroxide sulfate hydrate in the walls of the vent chimneys at 21 n epr occurs as a result of conductive heating of ambient seawater with only very minor amounts of mixing in contrast precipitation of amorphous silica in the vents must be due to conductive cooling of the hydrothermal solutions thus incremental reaction calculations demonstrate that reactions occurring in and associated with venting ridge crest hydrothermal solutions can be effectively modeled using the thermodynamic data and reaction modeling codes available today departures from equilibrium required to accurately model the mixing process are easily accommodated and consistent with data from the vents and vent forming materials

climate driven sea level anomalies modulate coastal groundwater dynamics and discharge 1 to better understand the physical drivers of submarine groundwater discharge sgd in the coastal ocean we conducted a detailed field and modeling study within an unconfined coastal aquifer system we monitored the hydraulic gradient across the coastal aquifer and movement of the mixing zone over multiple years at our study site sea level dominated over groundwater head as the largest contributor to variability in the hydraulic gradient and therefore sgd model results indicate the seawater recirculation component of sgd was enhanced during summer while the terrestrial component dominated during winter due to seasonal changes in sea level driven by a combination of long period solar tides temperature and winds in one year sea level remained elevated year round due to a combination of enso and nao climate modes hence predicted changes in regional climate variability driven sea level may impact future rates of sgd and biogeochemical cycling within coastal aquifers

brine pool deposition for the zn pb cu massive sulphide deposits of the bathurst mining camp new brunswick canada i comparisons with the iberian pyrite belt abstract the ordovician zn pb cu massive sulphide ore deposits of the bathurst mining camp share many features with those of the devonian carboniferous iberian pyrite belt particularly the tendency to large size tonnage and metal content shape as far as can be determined after allowing for deformation metal content particularly fe cu pb zn and sn mineral assemblages pyrite arsenopyrite pyrrhotite and lack or rarity of sulphates sulphide textures particularly framboidal pyrite lack of chimney structures and rubble mounds irregular metal or mineral zoning and the low degree of zone refining compared to hokuroku ores the major differences between the provinces are the lack of vent complexes and the presence of sn cu ores in the iberian pyrite belt there are also similarities in the geological setting of the two camps both lie within continental terranes undergoing arc continent and continent continent collision and in each case massive sulphide mineralisation followed ophiolite obduction the ore deposits are associated with bimodal volcanic rocks derived from morb and continental crust and marine shales and mineralisation was locally accompanied or followed by deposition of iron formations fluid inclusion data from veins in stockworks from at least six of the iberian massive sulphide deposits point to sulphide deposition having taken place in basins containing mostly spent saline ore forming fluids brine pools and it is suggested that most of the major features of the bathurst deposits can be explained by similar processes the proposed model is largely independent of ocean sulphate and o 2 content whereas low values of each are requisites for the current spreading plume model of sulphide deposition in the bathurst camp

oxygenation of the earth s atmosphere ocean system a review of physical and chemical sedimentologic responses abstract the great oxidation event goe is one of the most significant changes in seawater and atmospheric chemistry in earth history this rise in oxygen occurred between ca 2 4 and 2 3 ga and set the stage for oxidative chemical weathering wholesale changes in ocean chemistry and the evolution of multicelluar life most of what is known about this important event and the subsequent oxygenation history of the precambrian earth is based on either geochemistry or data mining published literature to understand the temporal abundance of bioelemental sediments bioelemental sediments include iron formation chert and phosphorite which are precipitates of the nutrient elements fe si and p respectively because biological processes leading to their accumulation often produce organic rich sediment black shale can also be included in the bioelemental spectrum thus chemistry of bioelemental sediments potentially holds clues to the oxygenation of the earth because they are not simply recorders of geologic processes but intimately involved in earth system evolution chemical proxies such as redox sensitive trace elements cu cr v cd mo u y zn and ree s and the ratio of stable isotopes 56fe 53cr 97 95mo 98 95mo 34s 33s in bioelemental sediments are now routinely used to infer the oxygenation history of paleo seawater the most robust of these is the mass independent fractionation of sulfur isotopes mif which is thought to have persisted under essentially anoxic conditions until the onset of the goe at ca 2 4 ga since most of these proxies are derived from authigenic minerals reflecting pore water composition extrapolating the chemistry of seawater from synsedimentary precipitates must be done cautiously paleoenvironmental context is critical to understanding whether geochemical trends during earth s oxygenation represent truly global or merely local environmental conditions to make this determination it is important to appreciate chemical data are primarily from authigenic minerals that are diagenetically altered and often metamorphosed because relatively few studies consider alteration in detail our ability to measure geochemical anomalies through the goe now surpasses our capacity to adequately understand them in this review we highlight the need for careful consideration of the role sedimentology stratigraphy alteration and basin geology play in controlling the geochemistry of bioelemental sediments such an approach will fine tune what is known about the goe because it permits the systematic evaluation of basin type and oceanography on geochemistry this technique also provides information on how basin hydrology and post depositional fluid movement alters bioelemental sediments thus a primary aim of any investigation focused on prominent intervals of earth history should be the integration of geochemistry with sedimentology and basin evolution to provide a more robust explanation of geochemical proxies and ocean atmosphere evolution

subsea floor replacement in volcanic hosted massive sulfide deposits abstract recent research on volcanic hosted massive sulfide vms deposits indicates that syngenetic subsea floor replacement ores form an important component of many deposits in the context of vms deposits subsea floor replacement can be defined as the syn volcanic formation of sulfide minerals within pre existing volcanic or sedimentary deposits by infiltration and precipitation in open spaces fractures inter and intra granular porosity as well as replacement of solid materials there are five criteria for distinguishing subsea floor replacement in massive sulfide deposits 1 mineralized intervals are enclosed within rapidly emplaced volcanic or sedimentary facies lavas intrusions subaqueous mass flow deposits pyroclastic fallout 2 relics of the host facies occur within the mineral deposit 3 replacement fronts occur between the mineral deposit and the host lithofacies 4 the mineral deposit is discordant to bedding and 5 strong hydrothermal alteration continues into the hanging wall without an abrupt break in intensity criteria 1 3 are diagnostic of replacement whereas criteria 4 and 5 may suggest replacement but are not alone diagnostic because clastic sulfide ores contain accessory rock fragments collected by the parent sediment gravity flow s during transport criteria 2 can only be applied to massive semi massive disseminated or vein style deposits and not clastic ores the spectrum of vms deposit types includes deposits that have accumulated largely subsea floor and others in which sedimentation and volcanism were synchronous with hydrothermal activity and precipitation of sulfides occurred at and below the sea floor over the life of the hydrothermal system deposits that formed largely subsea floor are mainly hosted by syn eruptive or post eruptive volcaniclastic facies gravity flow deposits water settled fall autoclastic breccia however some subsea floor replacement vms deposits are hosted by lavas and syn volcanic intrusions sills domes cryptodomes burial of sea floor massive sulfide by lavas or sediment gravity flow deposits can interrupt sea floor mineralization and promote subsea floor replacement and zone refining the distance below the sea floor at which infiltration and replacement took place is rarely well constrained with published estimates ranging from less than 1 to more than 500 m but mainly in the range 10 200 m the upper few tens to hundreds of metres in the volcano sedimentary pile are the favoured position for replacement as clastic facies are wet porous and poorly consolidated in this zone and at greater depths become progressively more compacted dewatered altered and less amenable to large scale infiltration and replacement by hydrothermal fluids furthermore sustained mixing between the upwelling hydrothermal fluid and cold seawater is regarded as a major cause of sulfide precipitation in vms systems and this mixing process generally becomes less effective with increasing depth in the volcanic pile the relative importance of subsea floor replacement in vms systems is related principally to four factors the permeability and porosity patterns of host lithofacies sedimentation rate the relative ease of replacement of host lithofacies especially glassy materials and early formed alteration minerals during hydrothermal attack and physiochemical characteristics of the hydrothermal fluid

intense silicification of footwall sedimentary rocks in the stockwork alteration zone beneath the brunswick no 12 massive sulphide deposit bathurst new brunswick intensely silicified volcaniclastic mudstones that underlie the brunswick no 12 massive sulphide deposit in northern new brunswick resemble silicified rocks described in the immediate footwall of many ancient and modern massive sulphide deposits the white to grey cryptocrystalline silica in the silicified rocks becomes more common with proximity to the vent and is most abundant immediately below the massive sulphide zone mass balance analysis of altered footwall sedimentary rocks on the 850 m level of the mine shows that sio2 increases up to 300 the high silica enrichment in the feeder zone is consistent with the presence of cherty silica in the massive sulphides and in associated exhalative iron formation coincident with silicification are enrichments in s feot mgo mno cao p2o5 f cl y cu co cr and ni as well as light rare earth elements and eu oxygen isotope analyses of chloritized and silicified footwall sedimentary rocks suggest that the hydrothermal fluid had a 18o composition o

the filon norte orebody tharsis iberian pyrite belt a proximal low temperature shale hosted massive sulphide in a thin skinned tectonic belt the filon norte orebody tharsis iberian pyrite belt is one of the largest pyrite rich massive sulphide deposits of the world the present structure of the mineralization consists of an internally complex low angle north dipping thrust system of variscan age there are three major tectonic units separated by thick fault zones each unit with its own lithologic and hydrothermal features they are internally organized in a hinterland dipping duplex sequence with high angle horses of competent rocks igneous and detritic rocks and massive sulphides bounded by phyllonites the mineralization is within the lower unit and is composed of several stacked sheets of massive sulphides and shales hosting a stockwork zone with no obvious zonation the intermediate unit is made up of pervasively ankeritized shales and basalts spilites here hydrothermal breccias are abundant the upper unit is the less hydrothermally altered one and consists of silicified dacites and a diabase sill the tectonic reconstruction suggests that the sequence is inverted and the altered igneous rocks were originally below the orebody carbon oxygen and sulphur isotopes in the massive sulphides and hydrothermal rocks as well as the mineral assemblage and the paragenetic succession suggest that the sulphide precipitation in the sea floor took place at a low temperature 150 c without indication at least in the exposed section of a high temperature copper rich event sporadic deep subsea floor boiling is probably responsible for the formation of hydrothermal breccias and the wide extension of the stockwork its co au enrichment is interpreted as being related with the superposition of some critical factors such as the relationship with black shales the low temperature of formation and the boiling of hydrothermal fluids the present configuration and thickness of the orebody is due to the tectonic stacking of a thin and extensive blanket 2 4 km2 of massive sulphides with low aspect ratio they were formed by poorly focused venting of hot modified seawater equilibrated with underlying rocks into the seafloor massive sulphide precipitation took place by hydrothermal fluid quenching bacteriogenic activity and particle settling in an unusual restricted euxinic and shallow basin brine pool with a low detritic input but with important hydrothermal activity related to synsedimentary extensional faulting resedimentation of sulphides seems to be of major importance and responsible for the observed well mixed proximal and distal facies the tectonic deformation is largely heterogeneous and has been mostly channelled along the phyllonitic tectonized shales deformation bands thus sedimentary and diagenetic textures are relatively well preserved outside the deformation bands in the massive sulphides superimposed variscan recrystallization is not very important and only some early textures are replaced by metamorphic tectonic ones the stockwork is much more deformed than the massive sulphides the deformation has a critical effect on the present morphology of the orebody and the distribution of the ore minerals this deposit is a typical example of the sheet like shale hosted anoxic low temperature and zn rich massive sulphides developed in a ensialic extensional basin

association between catastrophic paleovegetation changes during devonian carboniferous boundary and the formation of giant massive sulfide deposits abstract the iberian pyrite belt sw iberia is one of the largest sulfur anomalies in the earth s crust in the southern iberian pyrite belt more than 820 mt of exhalative massive sulfides were deposited in less than one million years at the devonian carboniferous boundary the shale of the ore bearing horizon contains biomarkers indicating major biogenic activity in a methanogenic setting including a five fold increase in typical vascular plant biomarkers and a significant anomaly in those probably indicating the presence of thermophilic archaea this contrasts with signatures in the average sedimentary rocks of the basin that indicate the sediments settled in oxic to sub oxic environments and that they have only minor biomarkers derived from continental paleoflora these data show that the formation of the mineralization was not only related to major hydrothermal activity synchronous with volcanism but may also have been controlled by the input of large amounts of organic matter mostly derived from the degradation of woodland detritus sourced in the nearby continent this massive influx of organic matter could have accelerated extremophilic microbial activity that used short chain hydrocarbons as electron donors for seawater sulfate reduction resulting in concomitant massive sulfide precipitation we propose that the giant massive sulfide deposits resulted from overlapping of geological and biological processes that occurred at the devonian to carboniferous transition including 1 continent collision during the onset of the variscan orogeny leading to major paleogeographic changes and volcanism 2 dramatic stress of continental ecosystems due to the combination of climatic change volcanism variations in the sea level and erosion on a regional scale 3 major biomass destruction and increase of organic supply to marine environments and 4 generation of anoxic conditions and the thriving of sulfate reducing microorganisms under these conditions massive sulfide deposits formed where venting sulfur poor but metal rich hydrothermal brines flowed into a hydrogen sulfide rich anoxic water column the data presented strongly suggest that there was a temporal and causal relationship between the devonian carboniferous geotectonic climatic and biological crises and the formation of the giant volcano sedimentary massive sulfide deposits of the southern iberian pyrite belt

zn pb cu massive sulfide deposits brine pool types occur in collisional orogens black smoker types occur in backarc and or arc basins volcanic hosted massive sulfide deposits of zn pb cu type were derived either from seawater dominated buoyant fluids that built mounds on the seafloor e g the ores of the hokuroku basin japan or from saline fluids that reversed buoyancy on mixing with seawater and filled basins on the seafloor e g several ores of the iberian pyrite belt and the mount read province in tasmania the hokuroku ores formed above subduction zones during protracted periods of regional extension but both the iberian pyrite belt and the mount read province formed under extensional stress during continent continent iberia or arc continent mount read collision and orogenesis in the iberian pyrite belt oblique convergence resulted in transcurrent faulting and this may also be the case for the mount read province transcurrent faulting may have allowed easy vertical access for the ore related magmas some of which were sourced in the asthenosphere as well as the blueschist and eclogitic facies emplaced in adjacent terrains and possibly also saline fluids exsolved from the magmas

giant pyritic base metal deposits the example of feitais aljustrel portugal detailed study of hanging wall rocks and alteration above the giant feitais orebody of aljustrel iberian pyrite belt portugal shows that cherts that constitute the immediate hanging wall to the sulfide deposit result from hydrothermal alteration of laterally equivalent fe and or mn rich jaspers textures geochemistry and lack of fossil radiolarians indicate that these jaspers are hydrothermal precipitates hydrothermal alteration of the jaspers took place concomitantly with sulfide precipitation through reaction with hot 150 c reduced fluids with replacement of hematite by magnetite pyrite and fe2 phyllosilicates on the basis of the above and considering also the results of previous studies on hydrothermal activity in the aljustrel volcanic rocks and sulfide ores we propose that sulfide precipitation may have taken place under a thin veneer of siliceous sediments present day massive sulfide formation in the guaymas basin and in the salton sea under hundreds of meters of sediments may be approximate analogues in the sense that the presence of a caprock reduces dispersion of black smoke and causes more efficient precipitation

integrated tectonic genetic model for volcanic hosted massive sulfide deposits volcanic hosted massive sulfide deposits exhibit a continuous range in metal composition from copper dominated cyprus type to lead rich zinc copper deposits kuroko type this spectrum is best viewed as a progressive enrichment in large ion lithophile elements lile in the ores e g pb ba and the magmatic systems e g k responsible for their generation thus lead rich volcanic hosted massive sulfide deposits are associated with calc alkalic magmatism in mature are systems e g buchans or in back arc sites where older continental crust can be implicated in magma genesis at the copper rich end of the spectrum ores are related to plagiogranites in supra subduction zone ophiolite complexes and lile enrichment is minimal the ancient back arc assemblages that now constitute greenstone belts host cu zn massive sulfide deposits associated with tholeiitic calc alkalic magmatic systems of intermediate lile enrichment i suggest that these variations in both the metal composition of such ores and the petrochemistry of coeval intrusions relate in a fundamental way to the siting of their emplacement in arc and back arc systems and the duration of the subduction process

salinity of oceanic hydrothermal fluids a fluid inclusion study abstract an extensive microthermometric study of quartz epidote plagioclase anhydrite and sphalerite hosted fluid inclusions from ophiolitic semail oman and trinity california ophiolites and oceanic east pacific rise hydrothermal vents gorringe bank odp leg 111 hole 504b crust has been carried out in order to constrain a model accounting for wide salinity variations measured in the oceanic hydrothermal fluids recorded salinities in fluid inclusions vary between 0 3 and 52 wt nacl eq however more than 60 of the mean standard deviation salinities of the samples are within the range 3 2 0 3wt nacl eq microthermometric error and the mean salinity of all fluid inclusions without the brines is 4 0 wt nacl eq with a standard deviation of 1 6 wt nacl eq whereas most samples display slightly higher salinities than seawater several samples exhibit very high salinities more than two times that of seawater these high salinities are restricted to the plagiogranites semail and trinity ophiolites which mark the top of the fossil magma chamber in the transition zone between the plutonic sequence and the sheeted dyke complex the fluid inclusion population studied in the plagiogranites is characterized by the occurrence of four major fluid inclusion families 1 low to medium salinity liquid vapor fluid inclusions which homogenize into the liquid phase 2 low salinity liquid vapor fluid inclusions with pseudocritical homogenization 3 low to medium salinity liquid vapor fluid inclusions which homogenize into the vapor phase and 4 high salinity liquid vapor halite fluid inclusions which homogenize into the liquid phase by halite dissolution and exhibit salinities as high as 52 wt nacl eq these fluid inclusion families are interpreted as resulting from phase separation occurring in hydrothermal or magmatic fluids within the transition zone between the hydrothermal system and the magma chamber at temperatures higher than 500 c very low salinities less than half that of seawater have been found only in one dioritic sample from the gorringe bank mineralogical and petrological data from the semail ophiolite shows the absence of cl rich minerals furthermore hydration of the crust although very important cannot account for the large salinity variations thus the large salinity variations measured are interpreted as resulting from phase separation and generation of brine rich fluids at the top of the magma chamber this phase separation and subsequent phase segregation and brine accumulation may result in a double diffusive convection of the fluids in the hydrothermal system

brine pool deposition for the zn pb cu massive sulphide deposits of the bathurst mining camp new brunswick canada ii ocean anoxia during mineralisation abstract current models of massive sulphide ore genesis in the bathurst mining camp new brunswick involve settling of sulphide particles from a stagnating low salinity hydrothermal plume spreading laterally in an anoxic ocean layer with minimal sulphate content there is fragmentary evidence of ocean anoxia in the form of local fine lamination in the shales that host some of the deposits but the total organic carbon s fe u th ni co v ni and v cr relationships indicate deposition under oxic or dysoxic conditions vanadium and mn values range from oxic to anoxic and sulphate reducing to non sulphate reducing but mn may be anomalously low due to derivation by erosion of acidic volcanic rocks the somewhat equivocal physical and chemical data combined with the likely disturbing effects of penecontemporaneous volcanism considerably weaken the case for an anoxic bottom layer in a static ocean the presence of barite with ambient seawater 34 s values in brunswick no 12 ore and the abundance of sulphate in modern euxinic basin waters make a sulphate free layer unlikely even if anoxic sulphate bearing low salinity fluids mixing with seawater would lead to growth of barite bearing chimneys and baritic rubble mounds which are not observed a model involving brine pool deposition better explains the major features of the bathurst ores

setting of zn cu au ag massive sulfide deposits in the evolution and facies architecture of a 1 9 ga marine volcanic arc skellefte district sweden the skellefte mining district occurs in an early proterozoic mainly 1 90 1 87 ga svecofennian magmatic province of low to medium metamorphic grade in the baltic shield in northern sweden the district contains over 85 pyritic zn cu au ag massive sulfide deposits and a few vein au deposits and subeconomic porphyry cu au mo deposits the massive sulfide deposits mainly occur within and especially along the top of a regional felsic dominant volcanic unit attributed to a stage of intense extensional continental margin arc volcanism from facies analysis we interpret the paleogeography of this stage to have comprised many scattered islands and shallow water areas surrounded by deeper seas all the major massive sulfide ores occur in below wave base facies associations however some ores occur close to stratigraphic intervals of above wave base facies associations and the summits of some volcanoes that host massive sulfides emerged above sea level intense marine volcanism was superceded at different times in different parts of the district by a stage of reduced volcanism uplift resulting in subregional disconformities and then differential uplift and subsidence resulting in a complex horst and graben paleogeography uplift of the arc is attributed to the relaxation of crustal extension and the emplacement of granitoids to shallow crustal levels a few massive sulfide ores formed within the basal strata of this second stage the horst and graben system was filled by prograding fluvial deltaic sediments and mainly mafic lavas and during this stage the skellefte district was a transitional area between renewed arc volcanism of more continental character to the north and subsidence and basinal mudstone turbidite sedimentation to the south this whole volcanotectonic cycle occurred within 10 to 15 m y we define 26 main volcanic sedimentary and intrusive facies in the skellefte district the most abundant facies are 1 normal graded pumiceous breccias which are interpreted as syneruptive subaqueous mass flow units of pyroclastic debris 2 porphyritic intrusions and 3 mudstone and sandstone turbidites facies associations define seven main volcano types which range from basaltic shields to andesite cones and rhyolite calderas despite this diversity of volcano types most massive sulfide ores are associated with one volcano type subaqueous rhyolite cryptodome tuff volcanoes these rhyolite volcanoes are 2 to 10 km in diameter 250 to 1 200 m thick at the center and are characterized by a small to moderate volume rhyolitic pyroclastic unit intruded by rhyolite cryptodomes sills and dikes massive sulfide ores occur near the top of the proximal near vent facies association the remarkable coincidence in space and time between the ores and this volcano type indicates an intimate genetic relationship between the ores and the magmatic evolution of the volcanoes many of the massive sulfide ores occur within rapidly emplaced volcaniclastic facies and are interpreted to have formed by infiltration and replacement of these facies some of the ore deposits have characteristics of both marine massive sulfides and subaerial epithermal deposits we suggest that massive sulfides in the skellefte district span a range in ore deposit style from deep water sea floor ores to subsea floor replacements to shallow water and possibly subaerial synvolcanic replacements facies models are provided for the mineralized rhyolite volcanoes and volcanological guides are provided for exploration for blind ores within these volcanoes

ferruginous and manganiferous haloes around massive sulphide deposits of the urals proximal brecciform ferruginous and manganiferous rocks related to vms deposits of the urals are subdivided into jasperites gossanites and umbers in addition to thin bedded jaspers and cherts the coherence of host rock composition and mn fe fertility of the sediments have been established fe poor pink hematitic and gray sulphidic chert are typical of the felsic class of vms deposits in contrast the contents of fe vary from high to moderate in ferruginous rocks enclosed in basaltic units associate with vms deposits fe and mn rich ferruginous rocks and umbers occur in association with limestones and calcareous sedimentary rocks in both types of volcanic sequences a common feature of jasperites and umbers is the abundance of replacement textures of hyaloclastites and carbonates by hematite and silica in addition replacement of clastic sulphides by hematite and magnetite is a characteristic genetic feature of gossanites all of these sedimentary rocks are accompanied by pseudomorphs of hematite and quartz formed after bacterial filaments the abundance of replacement textures are supportive of the halmyrolysis model in addition to hydrothermal sedimentary and sub seafloor hydrothermal replacement theories study of chemical zonation of altered hyaloclasts shows depletion of their rims not only in mobile na k mg but also in immobile al ti and ree whereas si and fe are concentrated in situ the halmyrolysis model presented here involving organic rich calcareous hyaloclastic sediments resolves the problem of subtraction of al ti ree and other elements which are commonly immobile under hydrothermal conditions the evolution of the halmyrolysis process from acidic reducing to alkaline oxidized conditions infers a possible range in transformation from fe ii mg smectites to fe silicates and fe si oxides as precursors of brecciform jasperite and thin bedded jasper the higher acidic initial stage of gossanite formation seems to be required for oxidation of organic matter and or pyrite the acidic condition facilitates the temporal preservation of immobile elements al ti ree in immature chlorite hematite gossanites another peculiarity of the gossanite forming processes is the likely sorption of p u and v by iron hydroxides displacing sulphides the general evolution of all ferruginous sediments results in complete fe 2 oxidation and silicification accompanied by subtraction of other elements the vertical diagenetic differentiation leads to concentration of mn carbonates silicates and oxyhydroxides into the tops of jasperite and gossanite layers mn oxyhydroxides scavenge positively charged hydrated cations like co and ni near vent bacterial communities may activate the processes of volcanic glass and sulphide degradation the proposed processes of halmyrolysis followed by silicification in situ may resolve the enigma of silica rich sediment formation in a silica undersaturated ocean the discrimination between gossanite and jasperite is useful for elaboration of new criteria for local exploration of vms and mn deposits halo dispersion of gossanites covering an area about two to three times that of the massive sulphide deposit is a good vector for ore body discovery proximal gossanites can be differentiated from jasperites by presence of relic sulphide clasts or elevated contents of chalcophile elements cu fe zn pb bi te as sb ba noble metals au ag and distinct ree patterns with la and eu positive anomalies the development of halmyrolysis and biomineralization models merit further elaboration and testing in on going research in order to add or revise theories of iron and manganese deposit formation 2012 elsevier b v

ore depositional process in the navan zn pb deposit ireland the navan zn pb deposit in ireland is hosted by a lower carboniferous carbonate dominated sedimentary sequence in excess of 97 percent of the ore is hosted by a courceyan shallow water succession termed the pale beds the ore occurs as complex strata bound tabular lenses often dislocated by faulting and truncated by a submarine erosional slide structure above this surface unconformity lies the economically minor but genetically important conglomerate group ore hosted by a complex debris flow termed the boulder conglomerate timing constraints on the mineralization can be defined by the relationship to the erosion surface and style of mineralization suggesting a late chadian or early arundian age approximately 345 ma the bulk of the ore formed below the erosion surface in the semilithified to lithified pale beds ore the mineralogy of the economic ores is relatively simple being dominated by sphalerite and galena in a 5 1 ratio pyrite and marcasite are present in subordinate amounts in the majority of the pale beds ore but dominate the conglomerate group ore and the pale beds ore immediately below the erosion surface particularly lens 2 1 gangue minerals are dominated by calcite dolomite and barite the morphology of the mineralization reflects subsea floor emplacement the orebody occurs as numerous strata bound horizons ranging from intense high grade massive sulfides to lower grade sulfide layers separated by barren limestone in all cases there is strong evidence for tectonic disruption during ore deposition sulfides were dominantly deposited as open space growth and replacement of host rock open space textures include dendritic skeletal stalactitic internal sediment geopetal and coarse bladed forms the general absence of coarse euhedral cavity lining textures or substantial collapse brecciation suggests that large cavities were not present prior to mineralization replacement textures range from delicate pseudomorphs of biodasts to more destructive granular styles sulfide sulfur isotope analyses exhibit two dominant groupings of delta 34 s from around 23 to 5 and 0 to 15 per mil respectively and a third minor grouping around 32 to 28 per mil at least two sources of sulfur are invoked values around 23 to 15 per mil are considered to be the result of bacteriogenic reduction of lower carboniferous seawater sulfate approximately 20ppm with a characteristic fractionation around 35 to 45 per mil away from sulfate this is the most common range of delta 34 s in the deposit values around 8 to 15 per mil are interpreted to be hydrothermal sulfide transported with the metal bearing fluid mixing of these two components is inferred from the isotopic data and trends in the mineral paragenesis barite has a mean of delta 34 s 21 or 2 per mil which falls within the range generally recognized for lower carboniferous seawater sulfate we consider that contemporaneous seawater sulfate was the dominant source of sulfur in the barite at navan implying that seawater accessed the pale beds at the time of mineralization

geochemical dynamics of the atlantis ii deep red sea ii composition of metalliferous sediment pore waters abstract the atlantis ii deep is an axial depression of the red sea filled with highly saline brines and covered by layered metalliferous sediment we report new data on the vertical distribution of major salts and trace metals dissolved in the pore waters of the metalliferous sediments we have studied the chemical composition of interstitial waters of two sediment cores of the western core 684 and southwestern core 683 basins the major dissolved elements are na and cl their concentrations are close to those of the brine overlying the sediment the pore waters are undersaturated with respect to halite at the in situ conditions 62 c 220 bars but are saturated at the shipboard conditions 10 c 1 bar the salt and water contents of the bulk sediment show that core 683 contained halite in the solid fraction a part of it precipitated after core collection but most of it was present in situ thermodynamic calculations with a water rock interaction model based on pitzer s ion interaction approach reveal that equilibrium between the pore waters and anhydrite is achieved in sediment layers for which observations report the presence of this mineral we used a transport model which shows that molecular diffusion can smooth the profile of dissolved salt and partly erase the pore water record of past variations of salinity in the lower brine for example we calculated that the pore water record of modern variation of brine salinity is rapidly smoothed by molecular diffusion the dissolved transition metals show large variations with depth in the interstitial waters the profiles of core 683 reflect the possible advection of hydrothermal fluid within the sediment of the southwestern basin the distribution of dissolved metals in core 684 is the result of diagenetic reactions mainly the reduction of mn oxide with dissolved fe ii the recrystallization of primary oxide minerals and the precipitation of authigenic mn carbonates