ORE PETROGRAPHIC ASPECTS OF RECENT BASALTIC ANDESITE FROM ARENAL VOLCANO, COSTA RICA

South-Central Section - 39th Annual Meeting (April 1–2, 2005)
Paper No. 12-8

Presentation Time: 8:30 AM-12:00 PM
ORE PETROGRAPHIC ASPECTS OF RECENT BASALTIC ANDESITE FROM ARENAL VOLCANO, COSTA RICA
BALL, Richard W. and GÖBEL, Volker W., Dept. of Geology, Stephen F. Austin State Univ, P.O.Box 13011 SFA, Nacogdoches, TX 75962-3011, sfageostud@hotmail.com Arenal volcano is the youngest of the subduction related andesitic strato volcanoes in the Guanacaste Range of NW Costa Rica. Its recent eruptive cycle started in 1968 and is presently characterized by lava dome formation in one of the summit craters. Blocks of dome rocks are continuously tumbling down the N-NW slope of the volcano as the dome is apparently expanding and its crust is breaking off. Samples studied are from a block fan at the N base of the Arenal and the lava flow of 1525. Arenal volcanites are holo- to hypocrystalline, plagioclase-phyric basaltic andesite rocks with pyroxene, clinoamphibole, and ore minerals. Magmatic ore mineralogy is dominated by magnetite of two generations. Older and larger magnetite is commonly associated with pyroxene phenocrystals. It may contain round inclusions of gold (2-7 microns dia.). Younger, smaller, and subhedral magnetite is an essential constituent of the groundmass. Partial to complete oxidation of magnetite in some rocks yielded hematite. It also formed by oxidative roasting of Fe-containing silicates.
South-Central Section - 39th Annual Meeting (April 1–2, 2005) General Information for this Meeting

Session No. 12--Booth# 8 Undergraduate Research (Posters) Trinity University: Fiesta Room, Coates University Center 8:30 AM-12:00 PM, Saturday, April 2, 2005 Geological Society of America Abstracts with Programs, Vol. 37, No. 3, p. 16
© Copyright 2005 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.