Analysis of potential field anomalies in Lavrion mining area, Greece

Abstract

Mining activities in Lavrion began during the first millennium B.C. after the decline of ancient Athens and then restarted more deliberately during the nineteenth century. Aeromagnetic data from a 1967 survey of the mining area was recompiled, processed, and interpreted for the present study. The original flight lines were digitized and leveled, and the international geomagnetic reference field (IGRF) was removed. The data were inverted by means of a terracing technique that defines separate domains of uniform distribution of physical properties that cause the magnetic anomalies. The log power spectrum was computed; along with the results of terracing, it suggested the existence of two sources of the magnetic anomaly. The long-wavelength anomaly reflects a large, concealed body that is most probably a granitic intrusion, consistent with local geological evidence. The source of the short-wavelength anomaly is a strongly magnetized body attributed to the net effect of various thin, magnetite-bearing sulfide zones. The anomalies were then separated in the wavenumber domain. Magnetic susceptibility measurements were made in situ on the exposed parts of the local formations. Three-dimensional models whose effect simulates the observed anomalies were calculated. Results of the modeling show that the large magnetic body is buried at 0.68 km depth. The small, relatively shallow body is about 0.035 km thick and buried at 0.6 km depth. The bodies do not show any corresponding gravity anomaly on the regional Bouguer gravity anomaly map.

CO 2 flow during orogenic gravitational collapse: Syntectonic decarbonation and fluid mixing at the ductile-brittle transition (Lavrion, Greece)

“…Relative rapid cooling of the pluton is constrained by K-Ar ages at 8.27 +/-0.11 Ma on biotite and at 7.3 Ma by apatite fission track (Altherr et al, 1982). Aeromagnetic data suggest that the Plaka pluton represents the exposed part of a larger batholith present at a depth of 600 to 700 m below the surface of the Lavrion peninsula (Marinos and Makris, 1975;Tsokas et al, 1998). The emplacement of this large batholith is potentially responsible for the genesis and circulation of metal-rich fluids leading to major ore deposition (Skarpelis, 2002;Voudouris et al, 2008a, b;Bonsall et al, 2011).…”

Syn- to post-orogenic exhumation of metamorphic nappes: Structure and thermobarometry of the western Attic-Cycladic metamorphic complex (Lavrion, Greece)

“…Lekkas et al (2011) proposed that this low-angle fault accommodated Miocene post-orogenic exhumation coeval with the emplacement of the Plaka granodioritic pluton (Pe-Piper and Piper, 2002;Stouraiti et al, 2010). Aeromagnetic data suggest that the Plaka pluton represents the exposed part of a larger batholith that might be present at depth throughout the Lavrion peninsula (Marinos and Makris, 1975;Tsokas et al, 1998). The crystallization of the granodiorite has been dated at 8.34 +/-0.2 Ma by U/Pb on zircon (Liati et al, 2009).…”

The Lavrion silver district: Reassessing its ancient mining history

“…First contact mineralisation is shown in plan projection in Figure 4a, together with Pounta contact mineralisation. It also shows surface outcrop of the Plaka granodiorite and associated hornfels, outcrops of thin granitoid and granodiorite dykes, and the limits of a deeper intrusion, some 15 km 2 in area, as interpreted from 20th‐century aeromagnetic data by Tsokas et al (1998). A striking feature of this map is the widespread distribution of first contact and Pounta contact mineralisation throughout the Lavrion district.…”