Microprobe Methods Research Articles

The nuclear microprobe as a tool in geology and mineral exploration

The nuclear microprobe is ideally suited to the microanalysis of geological samples where trace element quantitative microanalysis and imaging are essential. This review samples the broad application of nuclear microprobe methods in geological research that make use of the quantitative analysis capabilities of particle-induced X-ray emission (PIXE) and nuclear reaction analysis (NRA). It also discusses improvements in this technology, such as quantitative elemental imaging, and the potential of new nuclear microprobe techniques, such as channeling contrast microscopy (CCM) and ionoluminescence (IL), that complement PIXE and NRA and are being applied to geological problems.

The role of total-reflection X-ray fluorescence in atomic spectroscopy

Total-reflection X-ray fluorescence (TXRF) is a universal and economic method for the simultaneous determination of elements with atomic numbers > 11 down to the lower pg-level. It is a microanalytical tool for the analysis of small sample amounts placed on flat carriers and for contaminations on flat sample surfaces. Analyses of stratified near-surface layers are made possible by varying the incident angle of the primary beam in the region of total-reflection. This non-destructive method is especially suitable for thin layers of a few nanometres, deposited on wafer material although not usable as a microprobe method with a high lateral resolution. Furthermore, depth profiles of biological samples can be recorded by means of microtome sectioning of only a few micrometres, as, for example in the gradient analysis of human organs. In addition to micro- and surface-layer analysis, TXRF is effectively applied to element trace analysis. Homogeneous solutions, for example aqueous solutions, high-purity adds or body fluids, are pipetted onto carriers and, after evaporation, the dry residues are analysed directly down to the pg ml region. Particularly advantageous is the absence of matrix effects, so that an easy calibration can be carried out by adding a single internal standard element. A digestion or separation step preceding the actual determination becomes necessary if a more complex matrix is to be analysed or especially low detection limits have to be reached. A critical evaluation of the recent developments in atomic spectroscopy places TXRF in a leading position. Its outstanding features compete with those of e.g. electrothermal atomic absorption spectrometry (ETAAS), microwave induced plasma optical emission spectroscopy (MIP-OES) and inductively coupled plasma mass spectrometry (ICP-MS) in the field of micro- and trace analysis and with Rutherford backscattering (RBS) and secondary ion mass spectrometry (SIMS) in the surface-layer analysis.

Structure of Premixed Turbulent Propagating Flames Determined by Laser Tomography.

The structure of premixed turbulent flames in a constant-volume vessel was investigated using a microprobe method and laser tomography. The microprobe method was used to measure the flame propagation speed, the total thickness of the flame zone and the number of flamelets existing in the flame zone. Laser tomography was used to visualize the structure of the flame by passing a laser sheet (0.2 mm thick and 2 cm wide) through the turbulent flames to obtain their 2-D images. From the obtained images, islands of reactants as well as of products were found, at least in the 2-D images, when the turbulence intensity was above 0.4 m/s. Then, in order to obtain a rough measure of the thickness of the turbulent flame reaction sheet, the light intensity of the images was digitized and processed into three colors (black, gray and white), incorporating two appropriate threshold values in the analysis. The obtained mean thickness of the gray area, assumed to be the flame reaction sheet, showed a slight increase with turbulence intensity.

The mechanism of synthesis of titanium nitride by self-sustaining reactions

The mechanism of formation of titanium nitride by the self-propagating high-temperature synthesis was investigated. Samples were quenched in liquid argon at different stages of the reaction and analyzed by x-ray diffraction and electron microprobe methods. A mechanism is proposed in which the propagation of the reaction wave results in the formation of a thin surface layer of TiN and an unsaturated solid solution. The layer then dissolves to form a solid solution of nitrogen in titanium and then re-forms with continued reaction. On the basis of phase equilibria and diffusion information, an analysis is made in which the feasibility of the proposal mechanism is demonstrated.

The crystal structure of voggite, a new hydrated Na–Zr hydroxide–phosphate–carbonate mineral

AbstractThe crystal structure of the new mineral voggite, Na2Zr(PO4)(CO3)(OH).2H2O , from the Francon quarry, Montreal, Quebec, Canada, has been solved in order to determine the correct chemical formula, as conventional electron microprobe methods were found unreliable. The unit cell is monoclinic, I2/m, with a = 12.261(2), b = 6.561(1), c = 11.757(2)Å, β = 116.19(2)°. The structure consists of layers of edge-sharing Zr-O pentagonal bipyramids, separated by layers of Na-(O,H2O) octahedra. The carbonate ion acts as a bidentate ligand in the Zr-O polyhedron, the third oxygen atom being bonded to the Na atom. The phosphate group is bonded to three different Zr atoms and to a Na atom. The Zr-O bond lengths vary from 2.067 to 2.283 (mean 2.140Å), while Na-O are between 2.304 and 2.773, (σ = 0.006Å, mean 2.480Å). The carbonate and phosphate bonds are normal. It is inferred from the structure that the columns of octahedrally coordinated Na atoms can easily be broken apart when subjected to the heat generated by the electron microprobe beam, with the subsequent expulsion of water. This gives rise to ‘mobile’ Na atoms, which make quantitative electron microprobe analysis extremely difficult. The structure allows the ‘liberated’ Na atoms to move freely within planes parallel to .

Possible effects of grain-boundary REE on the REE distribution in felsic melts derived by partial melting.

Abundances of rare earth elements (REEs) in the whole rock and coexisting accessory minerals from a sample of the Cretaceous Naegi granite from central Japan, were determined with isotope dilution and electron microprobe methods. The granite contains the following amounts of accessory minerals: 853.8 mg fluorite, 215.2 mg apatite, 166.5 mg ilmenite, 145.5 mg zircon, 78.1 mg monazite, 10.5 mg fergusonite, 9.5 mg allanite, 3.6 mg rutile, 1.7 mg columbite and 1.4 mg thorite per 1 kg. REEs in the granite reside mainly in the accessory minerals, but the contribution of the accessories to the whole-rock REE abundance becomes less important toward the light REE end; the sum of REEs in the accessories accounts for only 53±6% of the whole-rock La, 59±6% Ce, 62±8% Nd, 66±10% Sm and 74±11% Gd-Yb. The unaccountable REEs in the rock are stored at the grain-boundaries of constituent minerals. The chondrite-normalized REE pattern for the grain-boundary (whole-rock minus sum of accessories) of the granite is light REE-enriched and consists of two linear segments with turning point at Gd. Since grain-boundaries are considered to melt first at partial melting, the early-formed melt will retain the REE characteristics of grain-boundaries. Some granitoids, which possess REE patterns consisting of two linear segments with turning point at around Gd and are considered to be formed by partial melting of crustal rocks, may have originated from source rocks with a grain-boundary REE distribution like that of the Naegi granite.

Studies on the mechanism of rubidium-induced kaliuresis

Renal clearance and electron microprobe methods were used 1) to elucidate the effects of chronic rubidium administration on potassium transport and 2) to localize, by the use of amiloride in acute experiments, the tubule site of interaction between rubidium and potassium. Substitution of drinking water by a 50 mM rubidium chloride solution for 9 to 11 days led to significant hypokalemia (plasma potassium 2.5 +/- 0.1 mM; plasma potassium plus rubidium 3.3 +/- 0.1 mM). Compared to a control group (reduction of plasma potassium to 3.4 +/- 0.1 mM by short-term potassium depletion) with a fractional potassium excretion of 2.1 +/- 0.3%, rubidium-treated rats excreted potassium at a much higher rate of 14.6 +/- 3.0%. The potassium content of principal cells was, however, significantly lower in rubidium-treated than in potassium-deprived animals. Similar to experiments in which rubidium was given acutely (3 hours), chronic rubidium administration was associated with preferential accumulation of rubidium in all tubule cells relative to potassium. Rubidium clearances were uniformly below those of potassium. Amiloride abolished the difference between rubidium and potassium clearances and sharply reduced the excretion of both cations. In view of the known site of action of amiloride, this suggests a distal tubule site of rubidium action on potassium transport. Amiloride also reduced or abolished the preferential uptake of rubidium into all but intercalated tubule cells. Marked cell heterogeneity of rubidium accumulation into intercalated cells was observed: One subpopulation, with low cell chloride, retained rubidium more effectively than another subpopulation with high cell chloride.

Energy-Dispersive X-ray analysis of the mineral content of corn bran treated in vitro and by passage through the pig Gastrointestinal tract

Energy-dispersive X-ray (EDX) analysis was tested as a method for examining the mineral contents of corn bran loaded in vitro or passed through the GI tract of pigs. Particles of dry-milled corn pericarp treated in vitro or retrieved from the stomach, ileum, and colon of killed pigs were prepared as microtomed bulk specimens directly embedded in resin. Because of heterogeneity caused by differences in substrate cell density and mineral content, X-ray count averages for a number of different specimens had a coefficient of variation greater than or equal to 0.24. Detectable amounts of K, Ca, S, and P, but not Na, Cu, Fe, or Zn were found in specimens of initial bran. Although detectable concentrations of Cu, Fe and Zn could be loaded in vitro, these elements generally were not detected in bran retrieved from the pig GI tract. During GI tract passage, sodium was loaded onto bran mainly in the small intestine and unloaded in the large intestine. Calcium was loaded in the stomach and unloaded mainly in the small intestine. At each GI tract location, content of Na, Ca, K, and P in retrieved bran was greater than in the initial bran. EDX microprobe methods can be applied successfully to plant tissues treated in vitro and in vivo to investigate interactions with minerals in a diet.

The mineralogy and metamorphic geology of low-grade metasediments, Northern Range, Trinidad

Forty-one low-grade metasediments from the Northern Range of Trinidad and from the neighbouring island of Tobago, West Indies, were investigated by microscopic, X-ray powder diffraction, Guinier camera technique and electron microprobe methods. The following minerals were encountered (in order of decreasing abundance): quartz, muscovite, chlorite, paragonite/muscovite mixed-layer, paragonite, organic material, calcite, pyrophyllite, dolomite, albite, hematite, chloritoid, pyrite, rutile, titanite, rectorite, stilpnomelane. The chemical composition of muscovite is dependent on the mineral assemblage, with Si = 6.1–6.2 per formula unit in two high alumina assemblages, versus Si = 6.6 in a low alumina assemblage. Microprobe analyses indicate that muscovite, paragonite and pyrophyllite are sometimes intergrown on a micrometre scale. Chlorite composition estimated from X-ray data shows good correspondence with microprobe data for two Al-poor samples but is less satisfactory for an Al-rich sample. Observed mineral assemblages in AKNa are indicative of the pyrophyllite-paragonite-albite fades. For the first time, chemical data for coexisting pyrophyllite, chlorite (M = MgO/(MgO+ FeO) = 0.377) and chloritoid (M = 0.110) are given. This assemblage is indicative of the low or medium pressure range of the lower greenschist facies. Pressure conditions during metamorphism are not well constrained but a minimum pressure of 2 kbar, corresponding to 5–6 km of overburden, can be estimated from the Na M4 content of actinolite. Temperatures derived from the calcite-dolomite geothermometer range between 300 and 350°C and are consistent with the presence of the assemblage pyrophyllite + calcite + quartz.

Inclusion pattern of non-conductive particles in electrodeposited nickel coatings

By combined X-ray electron microprobe and Dubpernell test methods, the relationship between the particles included in the nickel sublayer and the thickness-microporosity of the chromium plate was investigated. Whereas the metallographic and electron microscopic observations of the composite nickel layers provide information only about the total number of particles on the surface, the X-ray microanalysis makes it possible to distinguish particles that are not coated with a nickel layer, which can create micropores in the adjacent chromium layer. The number of open particles in the investigated plating system is less by an order of magnitude than the total number. Further studies using the Dubpernell test provided evidence that microporosity decreases as the chromium plate increases in thickness.

Ion Microprobe Determination of Rare Earth Elements in Perovskite from Kimberlites and Alnöites

AbstractIon microprobe analysis ofperovskite from kimberlites and alnöites permits the accurate determination of La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Er and Yb at the part per million level. Other rare earth elements (REE) are subject to interferences in the mass spectrum caused by matrix-derived molecular ions and cannot easily be determined with comparable precision. Chondrite-normalized plots of the ion probe REE data are smooth curves, confirming the superiority of this technique over electron microprobe methods at the levels of REE abundance found in these perovskites. The perovskites analysed contain between 2.8 and 7.1 wt. % REE oxides and are highly enriched in the light REE, having La/Yb ratios of 577–3229. These La/Yb ratios are not representative of the parental magmas but result from REE fractionation during crystallization of the perovskite. Parental magma La/Yb ratios are estimated to be of the order of 120–650. The lower La/Yb ratios (80–200) found for whole-rock kimberlites are considered to result from contamination by relatively heavy REE-enriched crustal material.

Chemical and isotopic evolution of hydrothermal solutions at Bingham, Utah

Systematic changes in mineral assemblages, mineral compositions, fluid inclusion characteristics, and hydrogen and oxygen isotope compositions in altered igneous rocks in the Bingham, Utah, porphyry copper deposit record the chemical and isotopic evolution of the hydrothermal solutions. Hydrothermal alteration in and surrounding the Bingham porphyry copper deposit consists of an outer propylitic zone of chlorite, epidote, and actinolite; a transition zone of hydrothermal biotite, actinolite, epidote, and chlorite; and an inner potassic zone of hydrothermal biotite and K-feldspar. Later sericitic and argillic alteration are superimposed on early potassic and propylitic alteration.Compositions of alteration minerals determined by electron microprobe methods are: biotite, mole fraction phlogopite (Mg/Mg + Fe) 0.58 to 0.83; actinolite, mole fraction tremolite (Mg/Mg + Fe) 0.58 to 0.79; epidote, mole fraction pistacite (Fe/Fe + Al) 0.27 to 0.30; and chlorite, mole fraction clinochlore (Mg/Mg + Fe) 0.66 to 0.76. Mineral compositions, especially MnO and MgO in chlorite, MnO in epidote, and TiO 2 in biotite, vary systematically with distance from disseminated ore. MgO in chlorite increases from 20.6 to 24.6 wt percent. MnO in chlorite and vein epidote increases from less than 0.1 to 0.59 wt percent and from 0.08 to 0.73 wt percent, respectively. The average mole proportion Ti in biotite increases from 0.1 to 0.24.Temperatures and salinities from fluid inclusions range from greater than 600 degrees C and 50 equiv wt percent NaCl for the potassic zone to approximately 370 degrees C and 33 wt percent for the propylitic zone. Coexisting liquid-rich and vapor-rich inclusions which homogenize at temperatures similar to the liquid and vapor phase, respectively, suggest boiling from the potassic core out to the potassic-propylitic transition zone. Compositions and homogenization temperatures for fluid inclusions suggest average P (sub (f)) -T conditions which vary smoothly from the potassic core to the propylitic fringe: 600 degrees C and 800 bars for the potassic zone, 450 degrees C and 500 bars for the transition zone, and 350 degrees C and 200 bars for the outer propylitic zone.Thermochemical calculations show that log f (sub H 2 O) decreases from 2.74 in the potassic core to 2.17 in the propylitic zone fringe, log f (sub S 2 ) decreases from -1 to -3.3 in the core to -8.7 in the propylitic zone, and log f (sub O 2 ) decreases from -16 to -17.5 in the core to -29 in the same interval. The log activity ratios of Ca, Mg, and K to hydrogen ion increase from the potassic to the propylitic zone. K (super +) /H (super +) increases from 3.1 to 3.4, Mg (super +2) /(H (super +) ) 2 ) increases from -2.25 to 4.25, and Ca (super +2) /(H (super +) ) 2 increases from less than 1 to 7.75.The extent of oxygen isotope exchange between the hydrothermal vein fluids and the igneous rock matrix in the Bingham stock increases with increasing temperature, abundance of alteration and quartz veins, thickness of veins, and fracture intensity. All these parameters generally increase inward from the propylitic zone into the core of the potassic zone. Within the potassic zone, there is pervasive exchange equilibrium between vein fluids and the selvage and rock matrix domains of the highly altered, veined, and fractured igneous rock. In contrast, vein fluids closely approach exchange equilibrium only with vein selvage in the propylitic zone; the igneous rock matrix has not equilibrated extensively, as might be expected in this lower temperature, less altered, and veined portion of the hydrothermal system.Calculated delta 18 O and delta D values of early fluids range from 6.8, -67 per mil in the potassic core to 5.1, -41 per mil in the outer propylitic zone, showing a systematic trend of 18 O depletion and deuterium enrichment with decreasing temperature outward from the innermost potassic zone. This trend is inconsistent with the progressive influx of local meteoric waters (delta D 18 O and delta D values for these fluids could have resulted from isotopic exchange between meteoric water and igneous rock at very low water (W)/rock (R) ratios over a range of temperature (> or =600 degrees -350 degrees C). Such water/rock exchange likely would be confined to deeper parts of the system with the exchanged fluids subsequently focused up into the present exposure of the deposit.Late-stage fluids responsible for sericitic and argillic alteration are progressively depleted in 18 O and deuterium, consistent with an increasing, and finally dominant, meteoric water component. If fluid-rock isotopic exchange has been the dominant mechanism in defining the isotopic compositions of the hydrothermal fluids at Bingham, then this later hydrothermal system was characterized by shallower circulation and higher water/rock ratios than was the system responsible for the development of the early hydrothermal fluids.

Electron microprobe analysis of micro amount powder samples: A case study on high purity coal

For the major, minor and trace element analysis of the inorganic compounds of a Ruhr-Saar coal different preparation techniques are investigated with X-ray fluorescence analysis, electron microprobe and classical wet chemical methods minimizing sample weight at standard preparation times and analytical accuracies. Considering accuracy as well as preparation efforts, determinations by electron microprobe on small sample amounts (<50 mg) proved to be superior to the other methods.

Studies of the structure of multicomponent Raney nickel catalysts

Genesis and structure of Raney nickel catalysts modified by Mo, Fe and Ca have been studied by XPS, SIMS and Auger and electron microprobe methods. It has been established that these catalysts are inhomogeneous and their structure can be described by models accounting for the interaction and localization character of metal components, their oxides and hydroxides.

Growth, characterization, and optical spectroscopy of Al2O3:Ti3+

The process of growing large diameter single crystals of Al2O3:Ti3+ by vertical solidification of the melt is described, and some of the problems in producing high-optical quality material are discussed. The characterization of the distribution and valance state of titanium ions was performed by x-ray techniques and laser Raman microprobe methods. The presence of other impurity ions, specifically iron, was also determined. In some cases titanium was found in the grown crystal to be in the rutile form. In addition, Ti-Fe pairs, and concentrated regions of titanium on the surface of the boule were also observed. Some procedures for minimizing these problems are discussed. The results of optical absorption, fluorescence, and lifetime measurements are reported. The addition of Fe is shown to produce a broad absorption band in the red region of the spectrum, and two-photon laser excitation terminating in the ultraviolet spectral region produces a broad blue emission band.

Light-dependent calcium release from photoreceptors measured by laser micro-mass analysis.

Yoshikami and Hagins first suggested that calcium is sequestered within membranous disks in the outer segments of vertebrate rods and that the bleaching of visual pigment molecules by light causes the release of Ca from the disks. Once released, the Ca was postulated to bind to Na+ channels or carrier molecules in the plasma membrane to produce the electrical response. This theory, termed the 'calcium hypothesis', is supported by much evidence but remains controversial, largely because of the difficulty in measuring calcium in rods and of demonstrating light-induced release. Here we describe direct measurements of total rod Ca using a new microprobe method, called laser micro-mass analysis, or LAMMA . Using this technique, we show that rods contain large amounts of Ca concentrated in their outer segments. Physiological levels of illumination produce a graded efflux of rod Ca content, amounting to about 10(4) ions per rhodopsin molecule bleached in dim light. As light does not change the rate of Ca influx, the total Ca content of the rod decreases. In bright light, as much as half the total Ca leaves the rod during only 1 min of illumination.

Cu-Ni-PGE mineralization at Romet�lv�s, Koillismaa layered igneous complex, Finland

Sulphides, tellurides and sulpharsenides, with special reference to the platinum-group minerals (PGM), have been studied from a subeconomic Cu-Ni-PGE mineralization encountered within the Syote section of the Lower Proterozoic (2.44 Ga) Koillismaa layered igneous complex (KLIC) in northern Finland using electron microprobe and ore-microscopical methods. The ore minerals occur partly as strata-bound patches and spots associated with spots of light-coloured secondary low-temperature silicates in the gabbronorite IV of the general igneous stratigraphic column of the complex and partly as a fine-grained impregnation in the penecontemporaneous basic sills and dykes. Among the PGM sperrylite, michenerite and a palladian bismuthian melonite have been encountered. The chemical composition is reported for these minerals as well as for the rest of the ore minerals (chalcopyrite, pentlandite, pyrrhotite, pyrite, sphalerite, cobaltite and hessite). It is concluded that volatile components played a significant role in the solution, transport and the final deposition of the sulphides and the PGM.

Chemical and structural changes induced by thermal annealing of shocked feldspar inclusions in impact melt rocks from Lappajärvi Crater, Finland

Plagioclase and microcline of clastic mineral and rock inclusions in impact melt rocks (kärnäite) were sampled from the coherent melt sheet located in the central crater area of the Lappajärvi meteorite crater and analyzed by optical, electron optical, X ray, and microprobe methods. Both types of feldspars display strong chemical, textural, and structural alterations compared to the feldspars of their parental crystalline basement rocks as a result of the thermal energy supplied by the surrounding superheated impact melt. Increase of shock experienced by the clasts prior to their incorporation into the melt results in increasing thermal alteration by the melt. In a lower degree of shock both primary plagioclase and microcline transform to ‘checkerboard’‐textured grains that consist of 5–10–μm‐sized subgrains of parallel optical orientation embedded in a mesostasis of eutectically grown sanidine and quartz. The subgrains are strongly zoned, disordered labradorite to andesine and rimmed by sanidine. In a high degree of shock the subgrains are larger and randomly oriented. The subgrains are the result of a nonequilibrium fractional crystallization from a liquid state during which a strong chemical exchange between the melt and the feldspar inclusions took place. On the basis of model calculations it is concluded that the temperature of the kärnäite melt at the time of the incorporation of the clastic debris was in the range of 1800° to 2100°C. The equilibration temperature of the clast‐melt mixture is estimated accordingly to be at least in the range of 1100° to 1140°C or higher, depending on the magnitude of the clast's postshock temperature. This temperature is above the solidus and in part above the liquidus temperature of a dry granodioritic melt and is also above the solidus temperatures of the feldspars. The clast‐laden melt was at rest when the equilibrium temperature was reached, suggesting that the readjustment of the transient crater cavity by central uplifting of the crater took place within a time scale of hours.

Desert varnish in Antarctica: A nuclear microprobe and backscattered 57Fe Mössbauer spectroscopic study

Nuclear microprobe analysis and backscattered 57Fe Mössbauer spectroscopic methods have been used to study the desert varnish surface coatings on samples of dolerite and sandstone from the Taylor Valley area of the McMurdo Dry Valley region, South Victoria Land, Antarctica. With the nuclear microprobe method the oxygen content of the varnish coating and underlying bulk rock was measured directly using the emitted protons from the 16O(d,p 1) 17O nuclear reaction, and also the 871-keV gamma rays emitted from the excited oxygen nucleus. In addition, the iron, calcium and sulphur contents were measured using their characteristic proton-induced fluorescent X-rays. The concentration profiles of these elements are presented in three- and two-dimensional diagrammatic representations. These show that in the Fe-containing dolerites, the desert varnish is formed by subsurface leaching of the Fe from the bulk rock. This is transported to the surface and deposited as a coating of hydrous ferric oxide, probably ferrihydrite, by subsequent oxidation and evaporation. In the essentially Fe-deficient sandstone, the Fe is derived externally from the overlying dolerite sills and is similarly transported and deposited as a varnish coating on the upper surfaces of the sandstone. Windblown inorganic salts, notably thenardite (Na 2SO 4) may be incorporated in the outer layers of the varnish. The backscattered 57Fe Mössbauer spectra recorded using both the conversion electrons and X-rays show that at a depth of ∼ 0.1 μm from the surface the predominant oxidation state of the Fe in the dolerite is Fe 3+, whereas at depths of 10 μm or more it is Fe 2+. For the sandstone it is present only as Fe 3+.

Mineralogical facies of a weathered serpentinized lherzolite from the Pyrenees, France

AbstractWeathering products of a serpentinized Iherzolite were investigated using optical microscopy, X-ray diffraction, infrared spectroscopy, and electron microprobe and wet-chemical analysis methods. The original mineral assemblage of the rock was chrysotile-enstatite-diopside-picotite-magnetite-calcite. Rock porosity governed the types of chemical microsystems from which the clay minerals were derived. These microsystems were grouped into three types. (1) Grain microcracks and grain boundaries. These were the earliest manifestations of weathering. Only pyroxenes were affected and transformed into talc + iron oxides. (2) Plasma zones in which the rock structure was preserved. The talc + oxide and chrysotile were both altered into a saponitic mineral. Picotite was oxidized to oxipicotite. (3) Fissure zones. In the argillized zones the rock was restructured. Saponite was altered to nontronite + magnesium silicate gel. Talc was also transformed to the same gel. Fissures were often filled with clay cutans and some were edged with iron oxides. Mineral facies in the different zones have been plotted in Si-R2-R3 coordinates.