Journal ArticleDOI
Genesis of Dioctahedral Phyllosilicates During Hydrothermal Alteration of Volcanic Rocks: I. The Golden Cross Epithermal Ore Deposit, New Zealand
Reads0
Chats0
TLDR
In this paper, the evolution of dioctahedral interstratified clay minerals in the Golden Cross epithermal deposit, New Zealand, was examined by optical microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission and analytical electron microscopies (TEM/AEM).Abstract:
To characterize the evolution of dioctahedral interstratified clay minerals in the Golden Cross epithermal deposit, New Zealand, hydrothermally altered volcanic rocks containing the sequence smectite through illite-smectite (I-S) to muscovite were examined by optical microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission and analytical electron microscopies (TEM/AEM). XRD analyses of 30 oriented clay samples show a broad deposit-wide trend of increasing illite content in I-S with increasing depth and proximity to the central vein system. Six representative samples were selected for SEM/TEM study on the basis of petrographic observations and XRD estimates of I-S interstratification. Ca and Na are the dominant interlayer cations in smectite, but as the proportion of illite layers in I-S increases, so does the K content and (IVAl + VIAl)/Si ratio. Layers and packets tend to flatten and form larger arrays, reducing the amount of pore space. Smectite coexists with (R = 1) I-S, rather than being (R = 0) I-S where R is the Reichweite parameter. The highest alteration rank samples contain discrete packets of mica to ∼300 A thick, but a limited chemical and structural gap exists between illite, which is intermediate in composition between common illite and muscovite, and illite-rich I-S. Selected-area electron diffraction (SAED) patterns of mica show that the 1M polytype dominates, rather than the common 2M1 polytype. Petrographic, SEM, and TEM data imply that all phyllosilicates formed via neoformation directly from fluids. Relatively mature I-S and micas form simultaneously, without progressing through the series of transformations that are commonly assumed to characterize diagenetic sequences during burial metamorphism in mud-dominated basins. Although the overall distribution of clay minerals is consistent with temperature as a controlling variable, local heterogeneities in the distribution of clay minerals were controlled by water/rock ratio, which varied widely owing to different rock types and fracture control.read more
Citations
More filters
Journal ArticleDOI
Dehydration of dioctahedral aluminous phyllosilicates: thermodynamic modelling and implications for thermobarometric estimates
TL;DR: In this article, a solid-solution model for dioctahedral aluminous phyllosilicates accounting for the main compositional variations, including hydration, was proposed.
Journal ArticleDOI
Epithermal Au-Ag and related deposits of the Hauraki goldfield, Coromandel volcanic zone, New Zealand
TL;DR: The epithermal Au-Ag vein deposits of the Hauraki goldfield in the Coromandel volcanic zone, New Zealand, produced 320,000 kg Au and 1.5 million kg Ag between 1862 and 2006 from a total land area of approximately 2,900 km2 as discussed by the authors.
Journal ArticleDOI
A reinvestigation of smectite illitization in experimental hydrothermal conditions: Results from X-ray diffraction and transmission electron microscopy
Eric Ferrage,Eric Ferrage,Olivier Vidal,Régine Mosser-Ruck,Michel Cathelineau,Javier Cuadros +5 more
TL;DR: Ferrage et al. as mentioned in this paper showed that illitization is a step mechanism involving four phases with increasing illite content, and that the influence of the starting material composition is a major limitation of Yates and Rosenberg's work.
Journal ArticleDOI
Illite-smectite mixed-layer minerals in felsic volcaniclastic rocks from drill cores, kakkonda, japan
TL;DR: In this paper, the illite-smectite (I-S) mixed-layer mineral series during alteration of felsic vitric materials in volcaniclastic sediments through two drill holes (IT-2 and IT-8) near the Kakkonda active geothermal system, Japan, were examined by optical microscopy, scanning and transmission electron microscopy (SEM and TEM), electron microprobe analysis, X-ray diffraction (XRD), and oxygen isotope analysis.
Book ChapterDOI
Chapter 14 Genesis of Clay Minerals
TL;DR: In this article, the authors describe the genesis of industrial clays and their diagenetic changes in different geological environments, such as weathering crusts and soils, continental and marine sediments, volcanic deposits, geothermal fields, wallrock alteration produced by intrusion of plutonic rocks and hydrothermal fluids, and very low grade metamorphic rocks.
References
More filters
Book
X-Ray Diffraction and the Identification and Analysis of Clay Minerals
TL;DR: The nature and production of x-rays diffraction effects structures, composition, properties and occurences of clay minerals sample preparation techniques for clay minerals identification of individual clay minerals and associated mineral identification of mixed layered clay minerals quantitative analysis as mentioned in this paper.
Journal ArticleDOI
Mechanism of burial metamorphism of argillaceous sediment: 1. Mineralogical and chemical evidence
TL;DR: In this paper, a detailed mineralogical and chemical investigation of shale cuttings from a well (Case Western Reserve University Gulf Coast 6) in Oligocene-Miocene sediment of the Gulf Coast of the United States was made by x-ray diffraction.
Journal ArticleDOI
Geothermal systems ancient and modern: a geochemical review
R.W. Henley,A.J. Ellis +1 more
TL;DR: Geothermal systems occur in a range of crustal settings as mentioned in this paper, including those occurring in regions of active or recently active volcanism, where magmatic heat at depths up to 8 km leads to convection of groundwater in the upper crust.
Journal ArticleDOI
Petrology of Philippine geothermal systems and the application of alteration mineralogy to their assessment
TL;DR: In this article, neutral-pH alteration is divided into four zones on the basis of key clay minerals, and two subzones are defined by calc-silicates, and the four main zones of acid alteration are: kaolinite (ambient to 120°C), dickite ± kaolite (120, 200, 200) and pyrophyllite ± illite (230,320°C).
Journal ArticleDOI
Ostwald processes and mineral paragenesis in sediments
John W. Morse,William H. Casey +1 more