ZEOLITE-BEARING AMYGDALOIDAL VOLCANIC AND VOLCANOCLASTIC ROCKS AT GABAL KATHERINE AREA, SOUTHERN SINAI, EGYPT

Abstract

The Gabal (G) Katherina complex in the southern Sinai of Egypt (Being a part of the ArabianShield) consisting mainly of volcanic arc granitoids, epiclastics and pyroclastic volcanic rocks (Rutiq volcanics), followed latterly by the emplacement of high-level intrusions (Katherina ring dyke) and calc-alkaline to slightly alkaline granites. The later-phase intrusions into the country rocks produced deferent degrees of contact aureole with significant alteration effects especially on the early-formed intermediate pyroclastics with their amygdules lava flows producing different degrees of zeolitization in the pyroclastic rocks, were investigated using Optical Microscopy, Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and wet chemical analyses. The studied volcanic rocks fall considerably in the basaltic andesite and rhyodacitedacite fields and show subcalcalkaline to calcalkaline affinities. On the other hand, the amygdaloidal volcanic rocks show low-temperature hydrothermal alteration characterized by the abundance of chloritization. Geochemically; Hf, Ta, Sr, Y, and Nb show slightly enrichment relative to the other zeolite-rich samples suggesting partial releasing of immobile elements from the volcanic rock during the alteration processes. Furthermore, zeolites found to fill the cavities in a non-uniform behavior. The subclass minerals such as phillipsite and chabazite have been accompanied by palagonite clasts, smectite, and calcite. Zeolites also occur in fibrous aggregates, partly or completely filling spheroid, ellipsoidal or irregular amygdules.