Volcanogenic Massive Sulphide Exploration Vectoring Using Interflow Argillite Horizons: Combining Data at Multiple Scales in the Kidd–Munro Assemblage (original) (raw)
Related papers
Proceedings of the IODP
The data presented in this report demonstrate significant improvements in the ability to constrain trace element and Sr isotopic concentrations in sediments overlying ridge-flank hydrothermal systems. Improved sampling methods orchestrated by the Integrated Ocean Drilling Program (i.e., advanced piston coring and anoxic sample processing) enabled the collection of reactive pore water species with minimal alteration and sampling artifacts. Improved methods of high-resolution inductively coupled plasma-mass spectrometry trace element analysis, including the use of the 8-hydroxyquinoline functional group to extract and preconcentrate rare earth elements and other trace metals, were used to compile a data set of 28 trace element concentrations and 87 Sr/ 86 Sr ratios. From this extensive data set, we were able to increase the current understanding of how redox-reactive species respond to diagenic processes. Near-basement trends were used in combination with the known composition of hydrothermal fluids that exit Baby Bare Springs to asses our ability to predict basement fluid compositions using sediment pore water profiles collected by deep-sea drilling. The results show that prediction of basement fluid composition is possible for many trace elements, provided the near-basement concentration gradients are minimal. In order to place the Ge/Si systematics in a broader context, pore water and borehole fluid Ge and Si data are presented from additional sites across the Juan de Fuca Ridge flank and from two additional ridge-flank settings. These data show that Ge concentrations and Ge/Si ratios are much higher in the basement fluids than in the basal sediments because of increased mobilization of Ge relative to Si within the basement hydrothermal reservoir. Solid-phase sediment data are presented, highlighted by the occurrence of Mn-and carbonate-rich layers.
2014
hydrothermal field (AAV) occurs within the Middle Valley sediment-filled rift on nortlern Juan de Fuca Ridge. The AAV is a rhomb-shaped zone of hydrothermally altered sediment 800 m by 350 m with moderate temperature venting (<276'C), associated witl anhydrite chimneys on hydrothermal mounds, and biota-rich areas associated with diffuse venting. Ten push-core samples (< 30 cm depth) were collected in and near the AAV by the submersible ALVIN during 1990 to examine the surficial nature of altered hemipelagic sediment and hydrothermal mounds. Within the AAV but away from active vent areas, weakly altered sediment is grey colored and indurated due to dissolution of calcareous nicrofossils and an increase in authigenic calcite and pyrite. Proximal to vent areas, intensely altered sediment is green colored, with an increased abundance of Mg-smectite, iron-bearing illite-smectite, pyrite, organic carbon and barite. Altered sediments contain elevated contents of MgO, total Fe2O3, MnO, S, Bu Zn, C't, Pb, As, Sb and Se, and are depleted in CaO and CO2 relative to unaltered sediment. Element enrichments and depletions increase toward active vent areas on hydrothermal mounds. Tilted hydrothermal crusts, and horizontal Mg-silicate veins seen in the cores, suggest that hydrothermal mounds grow by inflation, whereas chimney growth and collapse con8ibute a veneer of hydrothermal sediment. Sediment adjacent to an active chimney has layers of anhydrite, sulfide and nodular Mg-silicate. The sediment contains a high content of MgO and reduced S' and is tomposed of serpentine, saponite, talc, pyrrhotite, pyrite, gypsum, anhydrite, marcasite, sphalerite, chalcopyrite, isocubanite and galena. The upper layer reflects recent chimney collapse, whereas the sulfide layer represents a residual accumulation of past collapse evens. The abundance of Mg-silicates and limited biota suggest that recharge occurs over much of the mound surface, whereas discharge is focused at chimneys. Hydrothermal sediments in areas of difftrse venring are characterized by strong H2S odor, abundant quaxtz, amorphous silic4 barite, smectite, organic matter and biota. They differ from mound sediments by higber contents of Ba and SiO2, and lower contents of S and most chalcophile elements. These ateas may represent an incipient stage ofhydrothermal mound growth.
Rapid growth of mineral deposits at artificial seafloor hydrothermal vents
Scientific reports, 2016
Seafloor massive sulphide deposits are potential resources for base and precious metals (Cu-Pb-Zn ± Ag ± Au), but difficulties in estimating precise reserves and assessing environmental impacts hinder exploration and commercial mining. Here, we report petrological and geochemical properties of sulphide chimneys less than 2 years old that formed where scientific boreholes vented hydrothermal fluids in the Iheya-North field, Okinawa Trough, in East China Sea. One of these infant chimneys, dominated by Cu-Pb-Zn-rich sulphide minerals, grew a height of 15 m within 25 months. Portions of infant chimneys are dominated by sulphate minerals. Some infant chimneys are sulphide-rich similar to high-grade Cu-Pb-Zn bodies on land, albeit with relatively low As and Sb concentrations. The high growth rate reaching the 15 m height within 25 months is attributed to the large hydrothermal vent more than 50 cm in diameter created by the borehole, which induced slow mixing with the ambient seawater and...
Hydrothermal Lteration Associated with Massive Sulfide Deposits , Middle Valley . Northern
2006
Middle Valley is a sediment-covered rift near the northem extrenity of the Juan de Fuca Ridge. Hydrothermal fluids are presently being discharged at two vent fields about 3 km apart" Bent Hill (BtI) and the Area of Active Venting (AAV). At the AAV, the hydrothermal alteration consists of an inner, spatially restricted higber-temperature (>120'C)'zone (Zone I) that consists of grey, moderately to strongly indurated, and locally brecciated, fractured and veined sediment. Hydrothermal minerals within Zone I include a Mg-rich smectite-goup mineral, cblorite, amorphous silica, barite, pyrite and gypsum. Zone I is surrounded by a more widespread, lo\rer-temperature (<120"C) zone (Znne II) that consists of moderately indurated, bluegreen sediments that consist of a Mg-rich smectite-group mineral, carbonate, barite and minor pyrite. The zonal distribution of hydrothermal minerals is controlled by the chemical and physical evolution of high-temperature (tp ta 2i74'...
Journal of Geophysical Research, 2008
1] An active seafloor hydrothermal system subjects the background sediments of the Grimsey Graben (Tjörnes Fracture Zone) to alteration that produces dissolution of the primary volcaniclastic matrix and replacement/precipitation of sulfides, sulfates, oxides, oxyhydroxides, carbonates and phyllosilicates. Three types of hydrothermal alteration of the sediment are defined on the basis of the dominant hydrothermal phyllosilicate formed: smectite, kaolinite, chlorite. The most common alteration is near-total conversion of the volcaniclastic material to smectite (95-116°C). The dominant smectite in the deepest sediments sampled is beidellite, which is replaced by montmorillonite and an intimate mixture of di-and tri-octahedral smectite up core. This gradual vertical change in smectite composition suggests an increase in the Mg supply upward, the result of sediment alteration by the ascending hydrothermal fluids mixing with descending seawater. The vertical sequence kaolinite ! kaolinite-smectite mixed-layer ! smectite from bottom to top of a core, as well as the distinct zonation across the veins (kaolinite in the central zone ! kaolinite-smectite in the rim), suggests hydrothermal transformation of the initially formed smectite to kaolinite through kaolinite-smectite mixed-layer (150-160°C). The cause of this transformation might have been an evolution of the fluids toward a slightly acidic pH or a relative increase in the Al concentration. Minor amounts of chamosite fill thin veins in the deepest sections of some cores. The gradual change from background clinochlore to chamosite across the veins suggests that chamosite replaces clinochlore as Fe is made available from hydrothermal dissolution of detrital Fe-containing minerals. The internal textures, REE distribution patterns and the mode of occurrence of another magnesian phyllosilicate, kerolite, suggest that this mineral is the primary precipitate in the hydrothermal chimneys rather than an alteration product in the sediment. Kerolite precipitated after and grew on anhydrite in the chimneys. Oxygen isotope ratios are interpreted to reflect precipitation of kerolite at temperatures of 302°to 336°C. It accumulated in the hydrothermal mounds following the collapse of the chimneys and subsequent dissolution of anhydrite, thereby forming highly permeable aquifer layers underlying the vent field. Some kerolite was redeposited in the near vent field sediments by turbidity flows. The altered sediments are depleted in Mn, Rb and Sr, and enriched in U, Mo, Pb, Ba, As, Bi, Sb, Ag, Tl and Ga, as a result of leaching and precipitation, respectively. Conservative elements (Ti, Zr, Hf, Sc, Cr, Nb and Sn) are depleted or enriched in the altered sediments because of passive (precipitation or leaching of other phases) rather than active (because of their mobility) processes.
Seawater-metasomatism in hydrothermal sediments (Escanaba Trough, northeast Pacific)
Chemical Geology, 1995
Mydrothermall sediments from the NESCA vent-field, Escanaba Trough, are enriched in a 11 er of t Cd "vent-fluid" metals for which fluid data for the same, sediment-hosted, site exhibit anomalous etion. ese results are consistent with cooling of rising fluids and precipitation of various metal sulphide, sulphate and oxide phases in situ within the sediment column, prior to expulsion of the fluids from the seabed. Significant enrichments of Mg and U, elements which are quantitatively removed from high-temperature vent-fluids, are aiso observed in the Escanaba Trough sediments, however. Enrichments of these elements cannot derive from simple conductive cooling of the rising vent-fluids but, instead, are believed to result from extensive seawater-metasomatism as relatively fresh unreacted seawater is heated from below by hot sedimcn!s and/or percolating vcntfluids in the upper levels of the circulation system. Calculated seawater/sediment interaction ratios range from N 5: I to 2500 I of seawater per gram of sediment. Pb, Sr and Nd isotope distributions for the Escanaba sediments are consistent with combined sediment-fluid and seawater-sediment interactions. Pb isotope ratios fer hydrothermal and background sediments coincide with local sulphide deposits but are n~ch more radiogenic than local MORB. This indicates not only that complete isotopic re-equilibration must occur between the hot, rising fluids and the host sediments but, in addition, that sediment composition appears to dominate the Pb isotopic composition of these fluids. Sr and Nd isotope ratios in the hydrothermally altered sediments, which are distinct from background ratios, coincide closttly with modern seawater values, providing confirmatory evidence that extensive interactions must also have occurred between these hydrotherma! sediments and relatively fresh, unreacted seawater.
Chemical Geology, 2015
To determine the significance of metal fluxes from hydrothermal vents, understanding the speciation, reactivity, and possible transformations of metals and metal sulfides within the hydrothermal plume is critical. In this study, we measure the concentration and partitioning of trace metals (Fe, Mn, Cu, Cd, Co, Pb, Ni) and sulfide phases within the first 1.5 meters of the rising plume at three vent fields (TAG, Snakepit, and Rainbow) along the Mid-Atlantic Ridge. A combination HCl/HNO 3 leaching method was used to differentiate metals present in metal mono-sulfides from those in pyrite and chalcopyrite. At all three vent sites, Mn and Fe are primarily in the < 0.2 µm (filtered) portion, whereas Cu, Co, Cd, and Pb are mainly in the unfiltered fraction. Significant concentrations of HNO 3-extractable metals were found in the < 0.2 µm fraction at all three vent sites, indicating that they likely exist in a recalcitrant nanoparticulate phase such as pyrite or chalcopyrite. At TAG and Snakepit, Cu is correlated with Co, as Co enters into chalcopyrite and other CuFeS phases and Zn is correlated with Cd and Pb as they form discrete metal sulfide phases. At Rainbow, Zn, Cd, and Pb are correlated, but Cu and Co are not correlated. The Rainbow data are consistent with the higher metal to sulfide ratio found at Rainbow. These speciation differences are significant as both mineral type and size will affect the amount of metal transported from the vent site and its availability for biogeochemical processes.
Marine Geology, 2006
The Saldanha hydrothermal field is located at the top of a serpentinized massif (Mount Saldanha, MS) at a non-transform offset (NTO5) along the Mid-Atlantic Ridge (MAR), south of the Azores. It is one of the rare known sites on a worldwide basis where direct evidence of low-temperature (7-9 8C) hydrothermal activity has been provided by direct observation of hydrothermal fluid venting through small orifices in the ocean floor sedimentary cover. This study focuses on the mineralogy and geochemistry of 14 sediment cores collected at MS. For comparison, four samples collected at the Rainbow site (NTO6) were also studied. Mount Saldanha hydrothermal sediments are highly bdilutedQ within a dominant foraminiferal nanofossiliferous ooze with small fragments of underlying rocks. The mineral assemblage of the hydrothermal component is characterized by sulphides, nontronite, smectites, poorly crystallized Mn oxyhydroxides and amorphous material. Cu, Zn and Fe sulphides, Mn-Mg oxy-hydroxides and putative manganobrucite were also identified in one sample collected at an orifice vent. In this sample, micro-chimneys (conduits) composed of isocubanite and sphalerite were also identified. Mount Saldanha sediments show a clear enrichment in elements such as Mn, Mg, Fe, Cu, P and V, derived from hydrothermal fluids, and Ni, Cr and Co, derived from ultramafic rocks. The geochemical data together with the observed mineral assemblage suggest that the hydrothermal fluids are at a higher temperature than those measured at the escape orifices (7-9 8C), and a strong enrichment in Mg, mainly at the top of the mount, agrees with extensive mixing of the hydrothermal fluid with unmodified seawater. Nevertheless, the mineral assemblage of MS sediments is consistent with the precipitation from hydrothermal fluids at much lower temperatures than at Rainbow. The presence of serpentinized and steatitized (talcshist) ultramafic rocks and the occurrence of a strong methane anomaly within the overlying water column collectively suggest that the hydrothermal circulation at MS is driven by exothermic reactions closely associated with the serpentinization process. Rainbow sediments have a higher concentration in transition metals and consequently an enrichment in sulphides. These differences are likely to be a consequence of the higher temperature of hydrothermal fluids, reflected in the composition of hydrothermal solutions, and of a stronger hydrothermal flux at the Rainbow site. D