Major elements concentrations are controlled by the alteration and formation of minerals like feldspar-K, plagioclases, quartz, biotite, amphibole, chlorite, pyrite, wairakite
, prehnite, muscovite, epidote, and talc, as reported in CP by Elders et al.
Qualitative XRD analysis led to identifying a variety of zeolite species, including analcime, as the dominant zeolytic phase, followed by chabazite, natrolite, thomsonite, wairakite, stilbite, stilbite-Ca, phillip-site and stellerite-Na, thomsonite-Ca, chabazite-Ca and chabazite-Na, with minor stellerite, laumontite, levyne, phillipsite-Na, and gyrolite Other secondary minerals associated with zeolites were celadonite (Fe-rich mica), nontronite (Fe-rich smectite), greigeite (iron sulide mineral), koninckite or bobierrite (phosphates), alunite (sulphate), truscottite (silicate), calcite or dolomite, and quartz Nontronite occurred in most samples.
No regional zoning of zeolite assemblages was apparent in this study Figure 8 shows that the zoning sequence and textural evidence suggest the following crystallisation sequence: first K-rich clay (nontronite) followed by K-rich mica (celadonite), carbonate (calcite), cryptocrystalline silica (e g chalcedony), then thomsonite followed by chabazite, analcime, phillipsite and wairakite, and natrolite, laumontite, and stilbite-type minerals (stilbite and stellerite) Zeolites' stability ields are known from modern hydrothermal systems (Kristmannsdottir and Tomasson, 1978) and the observed sequence in the samples studied here conformed to a progressive decrease in temperature favouring hydrothermal system hydration.
Thomsonite is the most common zeolite phase formed after nontronite/celadonite Chabazite, analcime, phillipsite and probably wairakite are the irst zeolites which became crystallised.
The deep-sea volcanogenic accumulations interlayered with basalt effusives contain the following secondary silicates in semiquantitative relations: saponite > analcime, wairakite
> chlorite, actinolite, tremolite > heulandite, clinoptilolite (?), and talc (?).
The most common minerals present in the deposits are mordenite, clinoptilolite, laumonite, and wairakite
They are "heulandite" (heulandite sensu stricto and clinoptilolite), chabazite, analcime, stilbite, barrerite, epistilbite, gmelinite, laumontite, natrolite, mesolite, scolecite, stellerite, tetranatrolite, thomsonite, and wairakite. The first four minerals are the most common.
Wairakite is generally vitreous with well formed pseudo-octahedral to pseudo-icositetrahedral colourless crystals that can be confused with analcime (Fig.
Tetranatrolite, stellerite, barrerite, scolecite, and wairakite have also been identified.
At low temperature (<200[degrees]C), Na-Ca-bearing zeolites, trioctahedral (Ca)-Mg-Fe-bearing smectites, and calcite were stable, whereas at high temperature (>200[degrees]C), these minerals were replaced by chlorite-(Mg-Fe), albite, quartz, and Ca-bearing aluminosilicates, including epidote, wairakite, prehnite, and clinozoisite.
Increasing amounts of anhydrite were formed towards higher F/R ratios in competition with other Ca-bearing minerals such as epidote and wairakite until F/R values of >50 were reached, where all the Ca was consumed by the precipitation of anhydrite.
The mobility of Ca was controlled by the stability of carbonates, zeolites, and smectites at low temperature and by anhydrite, epidote, wairakite, prehnite, and clinozoisite at high temperature.