Contribution
Texture and composition of ferrian ilmenite from hornblende andesites of the Timok Magmatic Complex, Serbia
Luković, Aleksandar; Vulić †, Predrag; Zavašnik, Janez; Cvetković, Vladica; Šarić, Kristina; Banješević, Miodrag; Lazarov, Marina; Pačevski, Aleksandar
Neues Jahrbuch für Mineralogie - Abhandlungen Band 197 Heft 1 (2021), p. 65 - 83
54 références bibliographiques
publié: Jan 29, 2021
manuscrit accepté: Nov 3, 2020
revision du manuscrit reçu: Oct 29, 2020
révision du manuscrit demandée: Oct 5, 2020
manuscrit reçu: Jul 29, 2020
ArtNo. ESP154019701004, Prix: 29.00 €
Abstract
Ferrian ilmenite, representing an intermediate member of the hematite-ilmenite solid solution, is frequently present as an accessory mineral in hornblende andesites of the Timok Magmatic Complex (Serbia), which host world-class porphyry copper systems of the Bor Metallogenic Zone. In Krivelj, a type locality of this rock, ferrian ilmenite occurs in homogenous crystals without exsolutions present. Its unit cell parameters are a = 5.062(1) Å, c = 13.895(4) Å, V = 308.4(1) Å3 and according to the dependence of unit volume with composition, studied ferrian ilmenite corresponds to an intermediate member of the series with 53 mole% ilmenite (Xilm = 0.53). Transmission electron microscopy investigations show that this mineral is homogenous in terms of hematite-ilmenite solid solution and presence of exsolutions, even at the nanoscale level. Ferrian ilmenite from other localities (Majdanpek and Nikoličevo) shows various patterns of exsolution texture. Thus, ferrian ilmenite from Majdanpek shows very fine exsolutions of hematite-ilmenite phases. X-ray diffraction analysis confirms that initial ferrian ilmenite is broken down to two phases: a predominant host phase (ilmenohematite) with Xilm = 0.31 and a second exsolved phase (hemoilmenite) with Xilm = 0.78. Average grain compositions of this decomposed ferrian ilmenite correspond to a large degree to the previous homogenous ferrian ilmenite from Krivelj. However, due to slower cooling of andesite from the Majdanpek locality, a subsequent breakdown of the initial ferrian ilmenite was played out resulting in the formation of exsolution textures, that also caused changes in the magnetic properties of this mineral. In general, differences in ferrian ilmenite textures can imply the local variability in the conditions of the formation of the host volcanic rock and/or indicate that subsequent alteration processes have occurred.
Mots-clefs
hematite • ilmenite • hemoilmenite • ilmenohematite • solid solution • texture • exsolutions • andesite • porphyry copper • Timocite • Krivelj • Nikoličevo