Altered ilmenite

Strongly altered ilmenite with more than 70 wt.%... 

In this work, 6 Lac Tio waste rock samples are investigated 3 samples were freshly blasted waste rock and 3 were weathered samples from an old waste rock pile (approximately 25 years old) which underwent significant natural alteration. The ilmenite content varies from approximately 20 to 60 wt% in both... 

Leucoxene has a composition similar to that of rutile, and is a product of alterations of a number of titanium minerals, most often ilmenite and sphene. It contains higher amounts of titanium, compared to ilmenite, and can range from 61% to 75% Ti02. 

Most halloysite appears to be the result of supergene processes and, as noted by Ross and Kerr (1934), leaching by sulphuric acid, produced by the alteration of pyrite, appears to be one of the more common weathering processes. Alunite is commonly associated with halloysite (Ross and Kerr, 1934 Swineford et al., 1954). Sulphuric acid is commonly used to dissolve ilmenite in the manufacture of Ti02 (Willets and Marchett), 1958). It is possible that in nature it serves the same purpose. In the alteration of granitic rocks and pegmatites, feldspar is more likely to alter to halloysite... 

Secondary alteration of CAls in CO chondrites has been noted by a number of workers (Ikeda, 1982 Holmberg and Hashimoto, 1992 Tomeoka et al., 1992 Kojima et al., 1995 Russell et al., 1998). Nepheline is the most common replacement phase, with minor amounts of sodalite, ilmenite, and monticellite (Brearley and Jones, 1998). Russell et al. (1998) studied CAls in a suite of C03 chondrites ranging from petrologic type 3.0-3.7. They observed that CAls showed significant effects of alteration, such that, in some cases, all the primary components of the CAls have either been replaced or had their compositions modified. The key evidence of alteration includes increases in the FeO content of spinels in spinel-pyroxene inclusions, increased replacement of melilite by nepheline, sodalite, and diopside, and disturbed aluminum-magnesium systematics in some inclusions. 

The alteration of all but the most resistant primary minerals occurs in the mid- to upper saprolite zones in addition, less stable secondary minerals such as smectite are also destroyed. Serpentine, magnetite, ilmenite and chlorite are progressively weathered through the zone. Ferromagnesian minerals are the principal hosts for transition metals such as Ni, Co, Cu and Zn in mafic and ultramafic rocks they become leached from the upper horizons and reprecipitate with secondary Fe-Mn oxides in the mid- to lower-saprolite. 

Recently we have conducted Mossbauer studies of core-to-rim alteration of a deep sea basalt and a continental basalt (59 60). The ocean basalt from the Mariana- deep was altered by seawater, and several concentric layers with different colors could be recognized from core to rim. Based on the Mossbauer spectra and petrographic observation of these layers, chemical states of iron were characterized as ilmenite, titanomagnetite, and silicate minerals (59). The enhanced superpara-magnetic effect in the rim demonstrates that the rim of the sample pre-... 

The volcanic activity was followed by pneumatolytic and hydrothermal processes. Mineralization occurs in tuffites, quartz porphyries and arkosic shales and is represented by pitchblende, molybdenite, chalcopyrite, tetrahedrite, galena, sphalerite, arsenopyrite, magnetite, ilmenite, hematite and supergene minerals. Surprisingly, according to Ruzicka, there is no host-rock alteration. 

Anatase is a yellow, brown, reddish brown, green, blue or black titanium oxide mineral of composition Ti02. It commonly occurs as elongated bipyramidal crystals or octahedra (Dana, 1944) and hence it is also known as octahedrite. Anatase is the low temperature tetragonal polymorph of the other titanium oxide minerals, rutile (Legrand and DeviUe, 1953) and brookite (qq.v.), and its occurrence is restricted to areas which have been subjected to hydrothermal activity associated with acid volcanism, or metamorphism, where it forms in veins and cavities (such as Minas Geraes, Brazil). It is a frequent alteration product of other titanium-containing minerals such as sphene and ilmenite (q.v.). 

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