scholarly journals Mineralogical and Geochemical Constraints on the Origin of Mafic–Ultramafic-Hosted Sulphides: The Pindos Ophiolite Complex

Minerals ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 454 ◽  
Author(s):  
Demetrios G. Eliopoulos ◽  
Maria Economou-Eliopoulos ◽  
George Economou ◽  
Vassilis Skounakis
Keyword(s):  
Hydrothermal Alteration ◽  
Hydrothermal Systems ◽  
Ophiolite Complex ◽  
Magmatic Origin ◽  
Magnetite Ore ◽  
Sulphide Ores ◽  
Mineralogical Characteristics ◽  
Tectonic Contact ◽  
Geochemical Constraints ◽  
Complete Transformation

Sulphide ores hosted in deeper parts of ophiolite complexes may be related to either primary magmatic processes or links to hydrothermal alteration and metal remobilization into hydrothermal systems. The Pindos ophiolite complex was selected for the present study because it hosts both Cyprus-type sulphides (Kondro Hill) and Fe–Cu–Co–Zn sulphides associated with magnetite (Perivoli-Tsoumes) within gabbro, close to its tectonic contact with serpentinized harzburgite, and thus offers the opportunity to delineate constraints controlling their origin. Massive Cyprus-type sulphides characterized by relatively high Zn, Se, Au, Mo, Hg, and Sb content are composed of pyrite, chalcopyrite, bornite, and in lesser amounts covellite, siegenite, sphalerite, selenide-clausthalite, telluride-melonite, and occasionally tennantite–tetrahedrite. Massive Fe–Cu–Co–Zn-type sulphides associated with magnetite occur in a matrix of calcite and an unknown (Fe,Mg) silicate, resembling Mg–hisingerite within a deformed/metamorphosed ophiolite zone. The texture and mineralogical characteristics of this sulphide-magnetite ore suggest formation during a multistage evolution of the ophiolite complex. Sulphides (pyrrhotite, chalcopyrite, bornite, and sphalerite) associated with magnetite, at deeper parts of the Pindos (Tsoumes), exhibit relatively high Cu/(Cu + Ni) and Pt/(Pt + Pd), and low Ni/Co ratios, suggesting either no magmatic origin or a complete transformation of a preexisting magmatic assemblages. Differences recorded in the geochemical characteristics, such as higher Zn, Se, Mo, Au, Ag, Hg, and Sb and lower Ni contents in the Pindos compared to the Othrys sulphides, may reflect inheritance of a primary magmatic signature.

Hydrothermal Sr contamination of the Dippin sill, Isle of Arran, Western Scotland

1984 ◽  
Vol 48 (348) ◽  
pp. 311-322 ◽  
Author(s):  
A. P. Dickin ◽  
C. M. B. Henderson ◽  
F. G. F. Gibb
Keyword(s):  
Stable Isotope ◽  
Hydrothermal Alteration ◽  
Closed System ◽  
Hydrothermal Systems ◽  
Hydrothermal Fluids ◽  
Drill Core ◽  
Sr Isotope ◽  
Core Section ◽  
High Silica ◽  
Isotope Measurements

Abstract The Dippin sill, which is emplaced into the Triassic sediments of SE Arran, is an alkaline basic sheet which displays pronounced hydrothermal alteration. The 40-m-thick sill has suffered pervasive contamination with radiogenic Sr, introduced from the Triassic sediments by hydrothermal fluids. Stable isotope measurements suggest that fluids were of meteoric origin, but were restricted to a small closed-system circulation. Initial 87Sr/86Sr ratios in the sill were raised from an original value of 0.7032 to a maximum of 0.7091, contamination being especially pronounced near the contacts at Dippin Head itself (localities 12 and 14) and in a drill core section through the sill above Dippin. Hydrothermal Sr was incorporated into an early-formed high-CaO, high-Sr analcime, which replaced unstable high-silica nepheline in interstitial patches. However, this high-CaO analcime, along with plagioclase, was later replaced by a low-CaO, low-Sr analcime, allowing Sr leaching from the margins of the sill. Hydrothermal fluids are thought to have migrated up to 1 km laterally, up the dip of the sill, mainly via tension joints forming in the cooling intrusion. Pooling of hot fluids at the upper end of the sill probably raised water/rock ratios in this region and allowed greater Sr contamination during mineralogical alteration. The undersaturated mineralogy of the sill accounts for its pervasive hydrothermal Sr contamination, which contrasts markedly with the relatively undisturbed Sr isotope compositions of Hebridean granites involved in hydrothermal systems.

scholarly journals Habitability of hydrothermal systems at Jezero and Gusev Craters as constrained by hydrothermal alteration of a terrestrial mafic dike

Geochemistry ◽  
2020 ◽  
Vol 80 (2) ◽  
pp. 125613 ◽  
Author(s):  
Lacey J. Costello ◽  
Justin Filiberto ◽  
Jake R. Crandall ◽  
Sally L. Potter-McIntyre ◽  
Susanne P. Schwenzer ◽  
...  
Keyword(s):  
Hydrothermal Alteration ◽  
Hydrothermal Systems ◽  
Mafic Dike

Detection and monitoring of hydrothermal alteration by Principal Component Analysis applied on UAS derived optical data, Vulcano Island - Italy

2021 ◽  
Author(s):  
Daniel Müller ◽  
Stefan Bredemeyer ◽  
Edgar Zorn ◽  
Erica De Paolo ◽  
Thomas Walter
Keyword(s):  
Principal Component Analysis ◽  
High Resolution ◽  
Hydrothermal Alteration ◽  
High Efficiency ◽  
Principal Component ◽  
Component Analysis ◽  
Hydrothermal Systems ◽  
Unmanned Aircraft ◽  
Optical Data ◽  
Vulcano Island

<p>Modern UAS (unmanned aircraft system), light weight sensor systems and new processing routines allow us to gather optical data of volcanoes at a high resolution. However, due to the typically poor colorization, our ability to investigate and interpret such data is limited. Further, the information stored in the red, green and blue channel (RGB) is correlated. This makes any analysis a 3 dimensional task. Principal Component Analysis (PCA) helps us to overcome these problems by decorrelating the original band information and generating a variance representation of the original data. Therefore PCA is a suitable tool to detect optical anomalies, as might be caused by volcanic degassing and associated processes.</p><p>Applied in a case study at La Fossa Cone (Vulcano Island - Italy), the PCA showed a high efficiency for the detection and pixel based extraction of areas subject to hydrothermal alteration and sulfur deposition. We observed a broad alteration zone surrounding the active fumarole field, but also heterogeneities within, indicating a segmentation. Systematic variations in color and density distribution of sulfur deposits have implications for structural controls on the degassing system.</p><p>Combining the efficiency of PCA with the high resolution of UAS derived data, this methodology has a high potential to be employed in the spatio-temporal monitoring of volcanic hydrothermal systems and processes at surface.</p><p> </p>

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