Project

Discipline

hydrothermal; ophiolite; alteration; ore-deposit

Lead
Die chemische und physikalische Prozesse, die zur Entstehung von Kupfer- und Goldführende massiv-sulfidischer Erzlagerstätten am Meeresboden führen, sind gut bekannt nur wo sie direkt beobachtet werden können (z.B. beim Austritt heisser, metallreicher Fluid an "schwarzen Rauchern"). Dieses Projekt erforscht die Prozesse, die tief unterhalb des Meeresbodens ablaufen, anhand Gesteinen eines fossilen ozeanischen Krustenprofiles, das an Land aufgeschlossen ist.
Lay summary
Das fossile ozeanische Krustenstück befindet sich im Bergland vom Sultanat von Oman. Die Arbeiten im Gelände konzentrieren sich vor allem auf Gesteine, die mit dem hellgrünen Mineral Epidot angereichert sind, da diese Gesteine vermutlich den tiefen Ursprung (die "Wurzel") des erzbildenden Systems darstellen. Geologische Kartierungen, Probennahmen und diverse chemische und mineralogische Analysen werden durchgeführt. Die gewonnen Daten dienen anschliessend als Eingabe für Computersimulationen, die die erzbildenden Prozesse nachbilden sollen. Wir beabsichtigen die exakten chemischen Reaktionen zu bestimmen, die die Epidotanreicherung verursachen und wir werden den Einfluss dieser Reaktionen auf die Erzbildung am Meeresboden untersuchen. Zum Beispiel könnten unsere Forschungsergebnisse erklären warum einige kupferreiche Massivsulfide goldführend sind, andere aber nicht.  Wir erwarten, dass die Ergebnisse dieser Studie den Kenntnissstand über die fundamentalen Prozesse der Meerwasser - Gesteins Interaktion in der tiefen ozeanischen Kruste erweitern werden. Unsere Erkenntnisse könnten zudem Explorationsgeologen bei der weltweiten Suche nach massiv-sulfidischen Lagerstätten unterstützen.

Direct link to Lay Summary

Last update: 03.10.2016

Lead
Valuable accumulations of copper and gold ore are known to have formed on the ocean floor throughout much of Earth's history. Many details of the chemical and physical processes involved in forming these so-called "massive sulfide deposits" are well understood, because they can be observed today on the seafloor (for example, the discharge of hot, metal-rich solutions in "black smokers"). However, the steps of the formation process that occur deep below the seafloor cannot be observed directly, and so understanding is less clear. This project aims to investigate the deep features below massive sulfide deposits by examining a segment of the ancient oceanic crust that is exposed on the Earth's surface in the Oman mountains.
Lay summary
Field work in Oman will be targeted on rocks that consist largely of the bright green mineral epidote, as these presumably represent the deep roots of the ore-forming systems. Geological mapping, sampling and various chemical and mineralogical  analyses will be performed to provide input for computer simulations of the ancient ore-forming processes. We aim to identify the exact chemical reactions that produce the epidote-rich rocks and we will assess the influence of these reactions on processes that concentrate metals at the seafloor. For example, the results may shed light on why some of the copper sulfide deposits in Oman are gold-bearing, while others are not.  The results of this project will hopefully fill a gap in our understanding of the fundamental process of seawater-rock interaction deep in the oceanic crust. Our findings will also provide guidelines to industry geologists who are exploring various sites around the globe for this type of ore deposit.

Direct link to Lay Summary

Last update: 03.10.2016

Geochemical and rock magnetic data

Author	Belgrano, Thomas M.
Publication date	29.07.2019
Persistent Identifier (PID)	https://doi.org/10.1594/PANGAEA.899794
Repository	PANGAEA Data Publisher for Earth & Environmental Science
Abstract

Lava, dyke and volcanic glass samples from across the northern Semail ophiolite were collected to provide references for geological mapping of the Semail volcanic units. These samples were analysed by various geochemical means to assign them to a volcanic unit. In addition, the bulk rock magnetic properties of a subset of these samples were determined to aid interpretation of existing aeromagnetic data. The whole-rock major element and select trace element (Ba, Sr, Zr, Y, Zn, Cu, Ni, Cr, V, Sc) composition of the majority of these samples was determined by X-Ray fluorescence (XRF) at ETH Zürich using a PANalyticalTM Axios wavelength-dispersive instrument. Trace elements in a subset of these samples were further analysed by pressed-powder-pellet laser-ablation inductively-coupled plasma spectrometry (PPP-LA-ICP-MS) using a GeoLas-Pro 193 nm ArF Excimer™ laser system in combination with an ELAN DRC-e™ quadrupole mass spectrometer at the University of Bern. Where necessary for unit assignment, igneous clinopyroxenes in another subset of samples were measured by Electron microprobe (EMP) on a JeolTM JXA-8200 EMP at the University of Bern. A set of volcanic glasses were also analysed by EMP on the same instrument. Bulk magnetic susceptibility was determined by two methods: a handheld Exploranium KT-5 kappameter and a desktop Magnon kappameter at the Institute for Rock Magnetism (IRM), University of Minnesota. Duplicate analyses of the same samples with both instruments indicates good comparability between the two datasets. Natural remanent magnetization (NRM) was determined on a 2G Enterprises 760 RF TM SQUID superconducting rock magnetometer at the IRM.

Title	Year

Number	Title	Start	Funding scheme

This project is a direct continuation of an on-going SNF project with the same title. The planned research addresses water-rock interaction and mass redistribution in sub-seafloor hydrothermal systems within mafic oceanic crust. Among the features of these systems are extensive zones of rock alteration and associated volcanogenic massive sulphide (VMS) deposits, which are important metal resources for industry and which are targets of exploration worldwide. Current models of hydrothermal circulation in the oceanic crust suggest a direct genetic relationship between VMS deposits on the seafloor and deep, high-temperature hydrothermal reaction zones identified by epidote-rich rocks, "epidosites". However, this relationship remains untested and its basis is incompletely explained. We intend to clarify these issues by investigating the hydrothermal alteration in exposed oceanic crust in the Semail Ophiolite in northern Oman. Our on-going work in Oman has revealed abundant epidosites within the volcanic sequence and has laid the foundation for the present proposal. We solicit support from SNF to continue our project for a further 36 months by extending funding for 2 existing PhD candidates and 1 new PhD candidate, plus associated research and conference costs. One PhD candidate will continue to field mapping, interpreting satellite-SWIR imagery and analysing rock samples to produce lithological, structural and hydrothermal alteration maps of the extrusive sequence of the ophiolite and its underlying sheeted dike complex. This will enable reconstruction of the 3D geometry and hydraulic properties of hydrothermal flow paths at the equivalent depth of several km below the ocean floor. It will also provide a means to test for spatial correlations between deep footwall alteration and VMS deposits. A second PhD candidate will continue to analyse fluid inclusions in epidosites in order to characterize the physicochemical properties of the alteration fluids. This information will aid in reconstructing the chemical reactions that produce the mineral alteration, in tracing the origin of the fluids and in testing if they correlate chemically with fluids venting at the modern seafloor. Fluid inclusions in miarolitic cavities in tonalite intrusions will also be analysed to evaluate the extent to which magmatic fluids play a role in hydrothermal alteration of the oceanic crust and formation of VMS deposits. The third PhD candidate will use a reactive-transport code to conduct numerical simulations of the coupled thermal-hydraulic-chemical processes leading to the deep footwall alteration. The simulations will be constrained by input from the parallel field, geochemical and fluid inclusion studies in this project. This modelling is aimed at quantifying reaction mechanisms and fluxes of solutes and heat, providing a way to test scenarios for the origin of the input fluids and for their fate and relationship to VMS deposits once they exit the epidosites and migrate towards the seafloor.The products of this research project will be a series of conference presentations and publications in international, peer-reviewed, scientific journals. The results in these publications will be of practical significance to the exploration industry. In addition, the project we will have provided scientific training for the PhD candidates and several Master students.