Abstract

The zeolites ferrierite, mordenite, and clinoptilolite have formed with smectite through hydration reactions in a sequence of rhyolitic pyroclastic rocks near Lovelock, Nevada. High activities of silica and magnesia were required simultaneously for the large-scale crystallization of ferrierite in these diagenetically altered rocks. Post-depositional addition of Mg coincided with ferrierite and smectite formation. The source of the Mg is not known, but it could have originated either from a brackish, saline lake or from nearby leached basalts. Thus, origins of the Lovelock ferrierite deposit may have involved both lacustrine deposition and an open ground water system for the transformation of vitric tuffs into zeolites.

Ferrierite crystallized early, mainly in the pore space of the tuffs. Clinoptilolite and cristobalite grew later by replacement of glass shards. Orthoclase and mordenite crystallized somewhat later, orthoclase usually in intimate association with ferrierite in K-rich zones and mordenite alone in open pore spaces. Ferrierite crystallization proceeded through a mechanism of dissolution and reprecipitation on glass and clay surfaces. Significant variation in chemical composition of individual ferrierite crystals occurs on the scale of a few cubic millimeters.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not currently have access to this article.