A New Occurrence of Terrestrial Native Iron in the Earth’s Surface: The Ilia Thermogenic Travertine Case, Northwestern Euboea, Greece

Abstract

Native iron has been identified in an active thermogenic travertine deposit, located at Ilia area (Euboea Island, Greece). The deposit is forming around a hot spring, which is part of a large active metallogenetic hydrothermal system depositing ore-bearing travertines. The native iron occurs in two shapes: nodules with diameter 0.4 and 0.45 cm, and angular grains with length up to tens of µm. The travertine laminae around the spherical/ovoid nodules grow smoothly, and the angular grains are trapped inside the pores of the travertine. Their mineral-chemistry is ultra-pure, containing, other than Fe, only Mn (0.34-0.38 wt.%) and Ni (≤0.05 wt.%). After evaluating all the possible environments where native iron has been reported up until today and taking under consideration all the available data concerning the study area, we propose two possible scenarios: (i) Ilia's native iron has a magmatic/hydrothermal origin i.e., it is a deep product near the magmatic chamber or a peripheral cooling igneous body that was transferred during the early stages of the geothermal field evolution, from high temperature, reduced gas-rich fluids and deposited along with other metals in permeable structural zones, at shallow levels. Later on, it was remobilized and mechanically transferred and precipitated at the Ilia's thermogenic travertine by the active lower temperatures geothermal fluids; (ii) the native iron at Ilia is remobilized from deep seated ophiolitic rocks, originated initially from reduced fluids during serpentinization processes; however, its mechanical transport seems less probable. The native iron mineral-chemistry, morphology and the presence of the other mineral phases in the same thermogenic travertine support both hypotheses.

Fault identification for the catastrophic 1894 Atalanti earthquake using 3D finite-difference modelling and local geophysical data

“…Focal mechanisms also confirm the offshore occurrence of such faulting orientation (Benetatos et al, 2004). The occurrence of the Lichades-Kammena Vourla volcanic centre (Kanellopoulos et al, 2019) and the hot-springs on both coasts of the gulf (Kanellopoulos et al, 2018(Kanellopoulos et al, , 2020 are related to this tectonic setting.…”

Banded Iron Travertines at the Ilia Hot Spring (Greece): An interplay of biotic and abiotic factors leading to a modern Banded Iron Formation analogue?

“…Kanellopoulos et al. (, ) based on mineralogical and geochemical observations such as (a) the presence of elements in their native form, such as Fe, Pb, Cu, (b) the presence of native alloys such as Au±Cu‐Ag and the enrichment of metalloids such as As, Sb, and (c) the abundance of REE, suggested that the system has a magmatic contribution. As a result, metals and metalloids were mainly derived from magmatic fluids, which after mixing with heated sea waters deposited native elements, sulphide mineralization at depth, and As‐Fe‐rich travertines in the surface (Kanellopoulos et al., , ).…”

“…(, ) based on mineralogical and geochemical observations such as (a) the presence of elements in their native form, such as Fe, Pb, Cu, (b) the presence of native alloys such as Au±Cu‐Ag and the enrichment of metalloids such as As, Sb, and (c) the abundance of REE, suggested that the system has a magmatic contribution. As a result, metals and metalloids were mainly derived from magmatic fluids, which after mixing with heated sea waters deposited native elements, sulphide mineralization at depth, and As‐Fe‐rich travertines in the surface (Kanellopoulos et al., , ). The repeated measurements conducted during the last years (including wet and dry seasons, Kanellopoulos et al., ) have shown that the physicochemical parameters of the hydrothermal fluid are relatively stable with temperatures varying only from 60.9 to 63.7°C and pH values from 5.9 to 6.45 (Table , Figure ).…”

Mineralogy and Geochemistry of Ultramafic Rocks from Rachoni Magnesite Mine, Gerakini (Chalkidiki, Northern Greece)

“…The NiO content of olivines is rather low (<0.44 wt.%) and no Ni alloys were found during the microscopic study of the sample. Native Fe has been found in ophiolitic rocks such as serpentinized dunites, peridotites, serpentinites and chromitites [34]. In most cases, native Fe presence is associated with serpentinization, e.g., [35][36][37][38][39].…”