Zeolites in New Zealand and their use as environmental minerals

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Brathwaite, R.L. 2017 Zeolites in New Zealand and their use as environmental minerals. Lower Hutt, N.Z.: GNS Science. GNS Science report 2017/27 27 p.; doi: 10.21420/G2KP89

Abstract: In New Zealand, zeolitic rocks are found in hydrothermally altered rhyolitic pyroclastic rocks of Quaternary age in the Taupo Volcanic Zone (TVZ), marine tuffs and volcaniclastic sandstones of Miocene age in Northland and Auckland, and weakly metamorphosed marine tuffs and volcaniclastic sandstones of Triassic-Jurassic age in Southland and southwest Auckland. In the TVZ, extensive zeolite deposits occur in late Quaternary lacustrine vitric tuffs of the Ngakuru Formation. Individual zeolite deposits contain 50–80 volume % of zeolites over a thickness of up to 45 m in thinly stratified vitric tuffs and are localized along NE-trending normal faults. Glass shards in the tuffs are replaced by the silica-rich zeolites mordenite and clinoptilolite, along with cryptocrystalline silica (opal-CT), amorphous silica (opal A), K-feldspar, and smectite. The Miocene Waitemata Group hosts the zeolite minerals analcime, chabazite, clinoptilolite, erionite, mordenite, and phillipsite in volcaniclastic beds in the Auckland city area, and in correlatives of the Waitemata Group in Northland and at the northern end of the Coromandel Peninsula. They were formed by the alteration of volcanic glass in the volcaniclastic beds during diagenesis. Zeolitic tuffs and volcaniclastic sandstones occur in Triassic–Jurassic Murihiku Supergroup rocks in Southland and southwest Auckland. Laumontite is the dominant zeolite in volcaniclastic sediments of Late Triassic to Middle Jurassic age, whereas heulandite ± analcime ± stilbite ± phillipsite occur in in Middle–Late Jurassic sequences. The ion exchange, catalytic, and molecular sieve properties of zeolites, both natural and synthetic, makes them useful in a wide range of environmental applications. Two of the mordenite ± clinoptilolite deposits in the TVZ (Twist Road and Mangatete) near Ngakuru are being worked by Blue Pacific Minerals and uses include: absorbents for oil/chemical spills and animal wastes; stock feed additives; water treatment and filters; conditioners for sports turf and slow release fertilizer; stock rock for farm races. These uses are engendered by the high porosity (50–70%), high odour absorption, and moderate cation exchange capacity (90–120 cmol+/kg) of the zeolitic tuffs. Blue Pacific Minerals and Crown research institute Scion have recently developed a modified zeolite product (AQUAL-P), which scavenges phosphate from water and has wide applications in aquaculture and in the treatment of waste water and eutrophic lakes. There is also potential for use as cement/pozzolans because pozzolans such as zeolites can partially substitute for Portland cement, thus reducing the high-energy usage and CO2 emissions involved in the manufacture of Portland cement. (auth)