The hydrothermal alteration of feldspars in acid solutions between 300 degrees and 400 degrees C

Gruner, John W.

doi:10.2113/gsecongeo.39.8.578

Cited by 39 publications

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“…Observations of effects of solutions on rocks in present day solfataric and hot spring environments indicate that acid solutions bring about the formation of 1 : 1 clay minerals and alkaline solutions favor the formation of 2 : 1 clay minerals (Burbank, 1950 ;Fenner, 1936 ;Schmitt, 1950). Synthesis studies on clay minerals are in agreement with this generalization (Ewell and Insley, 1935;Gruner, 1944;Nell, 1934Nell, , 1936Nell, , 1944Roy and 0sborn, 1954).…”

Section: Of Alteration Mechanismsupporting

confidence: 76%

Argillization in the Cochiti Mining District, New Mexico

Bundy

1957

Clays clay miner. (Natl. Conf. Clays Clay Miner.)

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Volcanic and intrusive rocks (InMnly andesite and monzonite) of Tertiary age are associated with gold-and silver-bearing quartz veins. Hydrothermal alteration took place in two stages. The first and less intense alteration stage is associated with economic mineralization ; metallization during the second and more intense stage is limited to pyrite.Alteration zones from the vein outward include : (1) dickite, (2) iUite-kaolinite, (3) vermiculite-halloysite, and (4) Alteration of ferromagnesian minerals and plagioclase resulted largely in the tbrmation of 2 : I clay mineral types. Orthoclase is altered chiefly to illite and kaolinite. Dickite and quartz are end products of the most intense alteration in the area.Chemical analyses of the altered rocks in general show a decrease in basic ions toward the vein. Less significant changes are shown by acidic ions. Analyses of illites indicate that substitution of K by Na, Fe, Ca and Mg has taken place near the vein as shown K by an overall decrease in K K K and ratios. Both sodium and potassium seem Na' Fo' Ca Mgg to be instrtmaental in the formation of well-developed illite crystals.Alteration stages operative in the Cochiti district were developed by the action of solutions probably ranging in pg from 4 to 10. Alteration zones were formed ponecontemporaneously with gradual outward migration of the least intense zones.

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Section: Of Alteration Mechanismsupporting

confidence: 76%

Argillization in the Cochiti Mining District, New Mexico

Bundy

1957

Clays clay miner. (Natl. Conf. Clays Clay Miner.)

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“…Noll (1932) found the lowest temperature of formation to be 225°C, but the greatest amount formed at 250°C. Gruner (1944), on the basis of numerous experiments, concludes that muscovite (var. sericite) forms above 350°C, and kaolinite below.…”

Section: Temperatures Of Mineral Synthesismentioning

confidence: 99%

“…Morey and Ingerson (1937) synthesized adularia between 245°C and 300°C. Gruner (1936) has formed adularia (or orthoclase) by heating montmorillonite in gold-lined bombs in aqueous solutions of KHCOa (10%). Well-crystallized adularia was produced in 7 days at 300°C.…”

Section: Temperatures Of Mineral Synthesismentioning

confidence: 99%

Hydrothermal Alteration and Weathering

Kerr

2015

Geological Society of America Special Papers

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A considerable group of minerals, including the clay minerals, zeolites, pyrophyllite, chlorite, alunite, vermiculite, certain carbonates, sulfates, and other minerals under special circumstances, may originate through the interaction of thermal fluids and rock masses. The fluids consisting of heated waters, water vapor under pressure, acids, and frequently metallic ions originate well within the earth's crust as an aftermath of vulcanism. The reaction halos, aureoles, disseminations, and bleached zones in which the products of hydrothermal alteration are found represent the locale of reaction. In the interpretation of the origin of mineral deposits alteration areas are frequently as significant as associated intrusives.Alteration minerals form a group with unusual stability which exhibits a remarkable tendency toward convergence.The effects of weathering and the minerals produced are often similar to the products of hydrothermal alteration insofar as the hydrous silicates are concerned. Temperature and chemical environment are equally important as controlling factors in supergene processes as under hypogene conditions. The alteration effects may represent a single progressive epoch in a single rock type or may be due to different epochs embracing several types of wall rock. Alteration of younger igneous rocks may have a high argillic content, as in the Tertiary sequences of the western United States. On the other hand, alteration of old rock masses where regional metamorphism has been prevalent may yield a large content of chlorite of different types, hydromica, pyrophyllite, or serpentine. Both are more or less widespread hydrothermal effects in contrast to more local alteration such as zeolitization.The fluids responsible for aggregates of hydrothermal minerals have long since vanished. However, through a gradual accumulation of evidence on mineral synthesis, microscopic study of sequence, observations on thermal springs and fumaroles, a much improved picture of the conditions prevalent during hydrothermal alteration is emerging.The accumulation of field relationships becoming known through the studies of various observers places emphasis upon the relative role of wall rock in determining the nature and magnitude of alteration halos. Such factors as permeability, porosity, and conduits for fluid penetration assume an importance parallel to rock type. Essentially similar alteration aggregates may result from rocks as dissimilar as diorite and alaskite, while tremendous differences in the magnitude of the alteration halo may be noted between a porous tuff and a compact quartz monzonite even in the same district.Halos of hydrothermal alteration are frequently a prelude to metallic mineralization. This has been particularly noted in connection with certain tungsten-bearing veins, disseminated porphyry copper deposits, certain lead-zinc deposits, some goldbearing veins, and some uranium-bearing veins. In such deposits the metallic epoch is ordinarily closely associated with the culmination of hydrothermal activity....

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“…An experimental investigation on the decomposition of K-feldspar in aqueous solutions was carried out by Gruner (1944). This experiment was conducted in a large excess of 0.1 N HCI solutions at 300 ~ to 400~ The study of K-feldspar alteration in acid solutions under moderate temperature was performed by Norton (1939).…”

Section: Introductionmentioning

confidence: 99%

Formation of Mica During Experimental Alteration of K-Feldspar

Kawano

1995

Clays and clay miner.

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Abstract--Experimental alterations of K-feldspar in distiUed-deionized water at 150", 175", 200*, and 225*(2 were performed. The alteration products and dissolution mechanism of K-feldspar were examined by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS). SEM, TEM, and EDX clearly showed formation of fibrous boehmite less than 1.0 ~m in length at the early alteration stages. The boehmite fibers decreased in abundance and rounded platy 1 M mica was produced as alteration proceeded. The mica exhibited initially angular shaped small flakes of 0.69 tzm in average size, which developed to rounded platy particles of 1.97/~m. The main chemical reactions occurring in this experimental system can be expressed by: KAISi3Os + 6H20 + H + --~ AdO(OH) + 3H4SIO4 + K +, [K=feldspar] [boehmite]3 KAISi3Os + 12H20 ~ KA13Si3010(OH)2 + 2K + + 6H4SIO4 + 22H +.XPS showed no significant changes in intensities of photoelectron lines excited from K, Si, and A1 in the K-feldspar surface before and after alteration, however the K/Si molar ratios in the solutions were considerably smaller than that of the original K-feldspar. The results of XPS strongly indicate that no dealkalized layer was produced on the surface, and that dissolution of K-feldspar in aqueous solution proceeded congruently by a surface-reaction mechanism. The discrepancy of mass balance in the solutions may be mainly caused by adsorption of K on the surface of boehmite.

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The hydrothermal alteration of feldspars in acid solutions between 300 degrees and 400 degrees C

Cited by 39 publications

References 0 publications

Argillization in the Cochiti Mining District, New Mexico

Argillization in the Cochiti Mining District, New Mexico

Hydrothermal Alteration and Weathering

Formation of Mica During Experimental Alteration of K-Feldspar

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