Mixed-layer Chlorite-smectite Research Articles

The Pantelleria caldera geothermal system: Data from the hydrothermal minerals

This paper proposes, on the basis of petrographic and mineralogic data on cutting and cores from two deep wells (“Pantelleria 1” and “Pantelleria 2”), the first model of the active hydrothermal system of the island of Pantelleria. Phyllosilicates were studied in detail because they are considered key minerals in the identification of hydrothermal processes. The results of these studies emphasize differences between the intracaldera and pericaldera areas of the island. Within the 45 ka caldera there is a high-temperature (240–260 °C at 600–800 m depth) active hydrothermal system with five zones of characteristic alteration minerals with increasing depth. Rocks are unaltered to a depth of 200 m, contain smectite and mixed-layer chlorite-smectite (C/S) between 200 and 380 m, chlorite, illite, chalcedony and quartz from 380 to 500 m, albite, adularia and saponite from 500 to 680 m, mixed-layer biotite-vermiculite from 680 m to the depth drilled (1100). Outside the caldera, but near the rim, a low-temperature and low-permeability (< 140 °C) hydrothermal system is characterized by smectite, dolomite and ankerite at depths of 390 to 650 m, chlorite and calcite at 650–900 m, and mixed layers of chlorite-smectite, illite-smectite and iron carbonates (ankerite, siderite) from 900 m of the well at 1203 m. The superimposition of hydrothermal mineral assemblages is evidence for cooling in the hydrothermal system both inside and outside the caldera. We propose that a high-temperature hydrothermal system developed inside the caldera. In an early stage in the area surrounding the subvolcanic body, biotite isograd is reached and an alkali-metasomatism zone develops inside the body itself. This phase may also account for the development of a chlorite-albite-adularia zone extending to 400 m. A cooling phase (nearly 50 °C) followed, resulting in the substitution of biotite by mixed-layer biotite-vermiculite and by the crystallization of Fe-rich saponite instead of chlorite, within the currently active reservoir. A cooling phase has also been identified in the well outside the caldera.

Mafic Phyllosilicates in Low-Grade Metabasites. Characterization Using Deconvolution Analysis

AbstractThe &lt;2 µm clay fractions from low-grade metabasalts of eastern North Greenland are mixtures of mafic phyllosilicates and celadonite that show complex X-ray diffraction (XRD) patterns. Interpretation of such patterns is difficult and subjective using only visual examination of peak positions and shapes. Deconvolution analysis offers a less subjective means of identifying peak positions for overlapping peaks and is applied to several composite peaks in a pattern; the peaks identified are then rationalized in terms of specific mixed-layer phases. Comparison against NEWMOD patterns of the identified clay mixture provides an additional constraint on the phases identified. Three mafic phyllosilicates, discrete chlorite and two chlorite-smectites with 60:40 and 80:20 proportions are demonstrated in the same XRD pattern. Modelling using NEWMOD of a mechanical mixture between these mineral shows an excellent match to the observed XRD pattern. The recognition in low-grade metabasalts of chlorite and random and different varieties of regular mixed-layer chlorite-smectite offers support for the classical model of a tri-smectite to chlorite transition. This is in contrast to an alternative model proposing smectite and chlorite end-members with corrensite as a discrete phase crystallizing directly without intervening mixed-layer chlorite-smectite.

Layer Silicates from Serpentinite-Pegmatite Contact (Wiry, Lower Silesia, Poland)

AbstractHighly tectonized contact between serpentinite and younger pegmatite in the magnesite mine of Wiry contains various layer silicates. Vermiculite, chlorite, smectite, and interstratified mica-vermiculite were recognized by means of routine XRD examination. Two three component interstratifications of mica-vermiculite-chlorite and chlorite-swelling chlorite-smectite were identified by a combined procedure of deconvolution of the XRD patterns and simulation of XRD tracings. A mineral with large diffraction maxima, displaying “chlorite intergrade” characteristics, appeared to be a mixture of chlorite, mixed layer chlorite-smectite, and vermiculite. Polytypes of phyllosilicates were determined by the X-ray transmission method. Due to the heritage of parent mineral polytype structure by transitional products of alteration, two distinct sequences of layer silicates were observed: one formed from trioctahedral mica (vermiculite, mixed layer mica-vermiculite); and one evolved from chlorite (e.g., mixed layer chlorite-swelling chloritesmectite). A tentative scheme of the primary contact zone structure, not obscured by subsequent brittle tectonics either by transformation of layer silicates, is proposed.

The Clay Mineralogy of Calcitic Seat Earth in the Northern Everglades of Florida

ABSTRACT The interface between peat and underlying limestone bedrock in the Northern Florida Everglades is often occupied by an unlithified calcitic seat earth that is stratigraphically similar to coal-basin seat rock and contains a complex mineral assemblage composed of 14 different minerals. The distribution and characteristics of the clay-size fraction were used to indicate sediment-source areas, depositional environment, and the degree of alteration of the original mineral assemblage. X-ray-diffraction analysis of 42 samples showed that a significant lateral variation exists in the clay-mineral suite of seat earth with respect to location in the study area. The clay minerals palygorskite, sepiolite, and illite were found primarily towards the center of the study area and were derived from sediments north of the Everglades. Seat earth located along the basin flanks showed an increase in the abundance of mixed-layer smectite, kaolinite, and chlorite. The proposed source area for these minerals is from erosion of marginal marine-bar deposits that rim the basin. Underlying limestone bedrock erosion contributed to the detrital mineral assemblage but was not as important as source areas outside the basin. The study-area seat earth is interpreted to have been deposited in an alkaline environment that allowed much of the original detrital mineral assemblage to be preserved. The only exception to this was the occasional identification of well-crystallized, authigenic mixed-layer chlorite-smectite that occurred in samples located near the basin flanks, which were presumably deposited under more acidic conditions.

Development of rodingite in basaltic rocks in serpentinites, East Liguria, Italy

Hydrogrossular replacement of plagioclase in basaltic rocks enclosed in serpentinite, and relationships between hydrogrossular, pumpellyite, vesuvianite are described. Rogingitic rocks are dominated by mixed layer chlorite-smectite, chlorite, pumpellyite, hydrogrossular and vesuvianite. In these rocks pumpellyite attains maximal Mg contents, and chemical analysis shows extreme removal of Na2O, K2O, TiO2 and SiO2 from the basalts, and increase in the Fe3+/Fe2+ ratio. Leaching during serpentinization by extremely alkaline solutions dominated by Ca-Mg(OH) may explain removal of components, but the oxidation may suggest that at an earlier stage dykes may have acted as input aquifers.

Paragenèses minérales liées à des interactions basalte— sédiment— eau de mer (Sites 465 et 456 des Legs 65 et 60 du D.S.D.P.)

According to the data of deep-sea drillings, the «baking » of sediments at contact with basaltic units has been occasionally mentioned. In the studied samples, transformation of sediment leads to porosity reduction and authigenesis of zeolites (analcite, mordenite, wairakite) and clay minerals (saponite, mixed layer chlorite-smectite, chlorite). The effect of the thermal alteration is similar in sediments and underlying basalts : in both cases the mineral assemblages are contemporaneous and related to moderate-temperature fluids (90 °C to 250 °C).

Clay Minerals Associated with the Precambrian Gowganda Formation of Ontario

AbstractX-ray analyses indicate that chlorite, illite and mixed-layer chloritesmectite are present in the &lt; 2μ fraction of the Precambrian Gowganda Formation near Bruce Mines, Ontario. The mixed-layer material is restricted to the porous graywacke sandstones and is epigenetic in origin. The chlorite and illite are ubiquitous and may reflect high-grade diagenesis, low-grade metamorphism or a source rich in these minerals.