scholarly journals Internal Structure of a Seafloor Massive Sulfide Deposit by Electrical Resistivity Tomography, Okinawa Trough

2019 ◽  
Vol 46 (20) ◽  
pp. 11025-11034 ◽  
Author(s):  
K. Ishizu ◽  
T. Goto ◽  
Y. Ohta ◽  
T. Kasaya ◽  
H. Iwamoto ◽  
...  
Keyword(s):  
Electrical Resistivity ◽  
Internal Structure ◽  
Electrical Resistivity Tomography ◽  
Okinawa Trough ◽  
Massive Sulfide ◽  
Sulfide Deposit ◽  
Massive Sulfide Deposit ◽  
Resistivity Tomography ◽  
Seafloor Massive Sulfide

scholarly journals Subseafloor Alteration of a Modern Mafic-Volcaniclastic Hosted Seafloor Massive Sulfide Deposit

2020 ◽  
Author(s):  
Melissa. O Anderson ◽  
Mark Hannington ◽  
Timothy McConachy ◽  
John Jamieson ◽  
Thor Hansteen ◽  
...  
Keyword(s):  
Massive Sulfide ◽  
Sulfide Deposit ◽  
Massive Sulfide Deposit ◽  
Seafloor Massive Sulfide

scholarly journals Mineralization and Alteration of a Modern Seafloor Massive Sulfide Deposit Hosted in Mafic Volcaniclastic Rocks

2019 ◽  
Vol 114 (5) ◽  
pp. 857-896 ◽  
Author(s):  
Melissa O. Anderson ◽  
Mark D. Hannington ◽  
Timothy F. McConachy ◽  
John W. Jamieson ◽  
Maria Anders ◽  
...  
Keyword(s):  
Low Temperature ◽  
Massive Sulfide ◽  
Hydrothermal Fluids ◽  
Sulfide Deposit ◽  
Massive Sulfide Deposit ◽  
Remotely Operated Vehicle ◽  
Eruptive Fissure ◽  
Seawater Sulfate ◽  
Volcaniclastic Rocks ◽  
Seafloor Massive Sulfide

Abstract Tinakula is the first seafloor massive sulfide deposit described in the Jean Charcot troughs and is the first such deposit described in the Solomon Islands—on land or the seabed. The deposit is hosted by mafic (basaltic-andesitic) volcaniclastic rocks within a series of cinder cones along a single eruptive fissure. Extensive mapping and sampling by remotely operated vehicle, together with shallow drilling, provide insights into deposit geology and especially hydrothermal processes operating in the shallow subsurface. On the seafloor, mostly inactive chimneys and mounds cover an area of ~77,000 m2 and are partially buried by volcaniclastic sand. Mineralization is characterized by abundant barite- and sulfide-rich chimneys that formed by low-temperature (<250°C) venting over ~5,600 years. Barite-rich samples have high SiO2, Pb, and Hg contents; the sulfide chimneys are dominated by low-Fe sphalerite and are high in Cd, Ge, Sb, and Ag. Few high-temperature chimneys, including zoned chalcopyrite-sphalerite samples and rare massive chalcopyrite, are rich in As, Mo, In, and Au (up to 9.26 ppm), locally as visible gold. Below the seafloor, the mineralization includes buried intervals of sulfide-rich talus with disseminated sulfides in volcaniclastic rocks consisting mainly of lapillistone with minor tuffaceous beds and autobreccias. The volcaniclastic rocks are intensely altered and variably cemented by anhydrite with crosscutting sulfate (± minor sulfide) veins. Fluid inclusions in anhydrite and sphalerite from the footwall (to 19.3 m below seafloor; m b.s.f.) have trapping temperatures of up to 298°C with salinities close to, but slightly higher than, that of seawater (2.8–4.5 wt % NaCl equiv). These temperatures are 10° to 20°C lower than the minimum temperature of boiling at this depth (1,070–1,204 m below sea level; m b.s.l.), suggesting that the highest-temperature fluids boiled below the seafloor. The alteration is distributed in broadly conformable zones, expressed in order of increasing depth and temperature as (1) montmorillonite/nontronite, (2) nontronite + corrensite, (3) illite/smectite + pyrite, (4) illite/smectite + chamosite, and (5) chamosite + corrensite. Zones of argillic alteration are distinguished from chloritic alteration by large positive mass changes in K2O (enriched in illite/smectite), MgO (enriched in chamosite and corrensite), and Fe2O3 (enriched in pyrite associated with illite/smectite alteration). The δ18O and δD values of clay minerals confirm increasing temperature with depth, from 124° to 256°C, and interaction with seawater-dominated hydrothermal fluids at high water/rock ratios. Leaching of the volcanic host rocks and thermochemical reduction of seawater sulfate are the primary sources of sulfur, with δ34S values of sulfides, from –0.8 to 3.4‰, and those of sulfate minerals close to seawater sulfate, from 19.3 to 22.5‰. The mineralization and alteration at Tinakula are typical of a class of ancient massive sulfide deposits hosted mainly by permeable volcaniclastic rocks with broad, semiconformable alteration zones. Processes by which these deposits form have never been documented in modern seafloor massive sulfide systems, because they mostly develop below the seafloor. Our study shows how hydrothermal fluids can become focused within permeable rocks by progressive, low-temperature fluid circulation, leading to a large area (>150,000 m2) of alteration with reduced permeability close to the seafloor. In our model, overpressuring and fracturing of the sulfate- and clay-cemented volcaniclastic rocks produced the pathways for higher-temperature fluids to reach the seafloor, present now as sulfate-sulfide veins within the footwall. In the geologic record, the sulfate (anhydrite) is not preserved, leaving a broad zone of intense alteration with disseminated and stringer sulfides typical of this class of deposits.

scholarly journals Electrical resistivity tomography revealing the internal structure of monogenetic volcanoes

2013 ◽  
Vol 40 (11) ◽  
pp. 2544-2549 ◽  
Author(s):  
Stéphanie Barde-Cabusson ◽  
Xavier Bolós ◽  
Dario Pedrazzi ◽  
Raul Lovera ◽  
Guillem Serra ◽  
...  
Keyword(s):  
Electrical Resistivity ◽  
Internal Structure ◽  
Electrical Resistivity Tomography ◽  
Resistivity Tomography ◽  
Monogenetic Volcanoes

Pushing the limits of electrical resistivity tomography measurements on a rock glacier at 5500 m a.s.l. on the Tibetan Plateau: Successes and Challenges

2020 ◽  
Author(s):  
Nora Krebs ◽  
Anne Voigtländer ◽  
Matthias Bücker ◽  
Andreas Hördt ◽  
Ruben Schroeckh ◽  
...  
Keyword(s):  
Electrical Resistivity ◽  
Tibetan Plateau ◽  
Internal Structure ◽  
Electrical Resistivity Tomography ◽  
High Resistivity ◽  
Mountain Range ◽  
The Tibetan Plateau ◽  
Rock Glacier ◽  
Resistivity Tomography ◽  
Rock Glaciers

&lt;p&gt;Geophysical methods provide a powerful tool to understand the internal structure of active rock glaciers. We applied Electrical Resistivity Tomography (ERT) to a rock glacier at an elevation of 5500 m a.s.l. in the semi-arid Nyainq&amp;#234;ntanglha mountain range on the Tibetan plateau, China. &amp;#160;The investigations comprised three transects across the rock glacier and its catchment, each spanning over a distance of 296 m up to 396 m, equipped with 75 up to 100 electrodes respectively. Our measurements were successful in revealing internal structures of the rock glacier, but were also accompanied by challenges.&lt;/p&gt;&lt;p&gt;We successfully detected first-order permafrost structures, such as a shallow about 4 m thick active layer of low electrical resistivity values that was underlain by potentially ice rich zones of high resistivity. Further high-resistivity zones were found and interpreted as dense bed rock of adjacent slopes that undergird the loose rock glacier debris.&lt;/p&gt;&lt;p&gt;Challenges, we faced in the application of ERT, were mainly posed by the morphology and internal structure of the rock glacier itself. Coarse debris created a rough surface that prevented a uniform setup with accurate 4 m spacing. The presence of loosely nested blocks of pebble size up to boulders with large interspaces resulted in high contact resistances. The consequent low injection current densities and possible noisy voltage readings downgraded part of the data, causing low data density and resolution. Coupling was partly improved by attaching salt-watered sponges to the electrodes and adding more conductive fine-grained materials to the electrodes. The detected high resistivity ice layer impeded deep penetration of electrical currents, which caused that the lower limit of the permanently frozen zone could not be defined.&lt;/p&gt;&lt;p&gt;Despite these challenges, the captured ERT profiles are an indispensable contribution to the sparse field data on the internal structure of rock glaciers on the Tibetan plateau. Our results contribute to a better understanding of the prospective evolution of rock glaciers in dry, high mountain ranges under a changing climate.&lt;/p&gt;

Internal structure and conditions of permafrost mounds at Umiujaq in Nunavik, Canada, inferred from field investigation and electrical resistivity tomography

2008 ◽  
Vol 45 (3) ◽  
pp. 367-387 ◽  
Author(s):  
Richard Fortier ◽  
Anne-Marie LeBlanc ◽  
Michel Allard ◽  
Sylvie Buteau ◽  
Fabrice Calmels
Keyword(s):  
Electrical Resistivity ◽  
Internal Structure ◽  
Prior Information ◽  
Electrical Resistivity Tomography ◽  
Reference Model ◽  
High Resistivity ◽  
Unfrozen Water ◽  
Resistivity Tomography ◽  
Unfrozen Water Content ◽  
Resistivity Model

A systematic approach was used for the interpretation of the electrical resistivity tomography carried out on two permafrost mounds at Umiujaq in Nunavik, Canada, to assess their internal structure and conditions. Prior information under the form of a geocryologic model of the permafrost mounds was integrated in the inversion of the pseudo-section of apparent electrical resistivity. The geocryologic model was developed from the synthesis of previous field investigations, including shallow and deep sampling, temperature and electrical resistivity logging, and cone penetration tests performed in the permafrost mounds. Values of electrical resistivity were ascribed to the different layers making of the geocryologic model to define a synthetic resistivity model of the permafrost mounds used as a reference model to constrain the inversion. The constrained resistivity model clearly show the presence of ice-rich cores in the permafrost mounds underscored by high resistivity values in excess of 30 000 Ωm, while the unfrozen zones surrounding the permafrost mounds are characterized by resistivity values lower than 1000 Ωm. The spatial distribution of unfrozen water and ice contents in the permafrost mounds were also assessed according to empirical relationships between the electrical resistivity and water contents. The ice content is highly variable and can be as high as 80% in the ice-rich cores, while the unfrozen water content varies between 2% and 5%. The integration of prior information in the inversion process leads to a more realistic constrained resistivity model showing sharp resistivity contrasts expected at the boundaries such as the permafrost table and base.

scholarly journals Geology and Geochemistry of the VOLPA Seafloor Massive Sulfide Deposit, Niua Volcano, Tonga

2020 ◽  
Author(s):  
Talia Moum ◽  
Melissa. O Anderson ◽  
John Jamieson ◽  
Richard Parkinson ◽  
Elizabeth Austin
Keyword(s):  
Massive Sulfide ◽  
Sulfide Deposit ◽  
Massive Sulfide Deposit ◽  
Seafloor Massive Sulfide
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