Minerals accessory

The hard rock deposits are mined mainly for feldspar with mica and quartz being accessory minerals. These deposits are extensive, often covering hundreds of square meters and are recognized by the light-colored, granite-like appearance with shiny mica flakes being a prominent feature. The mica content of these deposits ranges from approximately 6—10 wt %. 

Talc of metasedimentary origin is formed by hydrothermal alteration of a dolomitic host rock by a silica-containing fluid. This type of deposit is typical of Montana and AustraUa. It is usually quite pure with talc content of 90 to 98% and often very white as well. Dolomite [17069-72-6], CaMg(C02)2, is the most common accessory mineral. The fourth type is of metamorphic origin, where a siUcaceous dolostone is first converted to tremolite [14567-73-8] or actinohte [13768-00-8] and then partially converted to talc. The Balmat, New York, and Death Valley, California, deposits are of this type. Tremolite, dolomite, and serpentine are common accessory minerals. This type of talc deposit has a variable talc content (30—80%), but is usually white and often commercially exploited because of the properties of its accessory minerals rather than the talc. 

ACCESSORY MINERAL GRAINES AS A TOOL FOR THEIR TOTAL Pb AGE DATING... 

MATHEMATICAL BASIS AND SOFTWARE FOR SINGLE GRAIN MILLIPROBE XRF TRACE ELEMENT ANALYSIS (XRF-MP/SG) OF ACCESSORY MINERALS... 

The elements for which the results can be underestimated because of an incomplete digestion of refractory accessory minerals such as zircon and garnet, and/or formation of insoluble fluoride complexes have been distinguished. Recommendations on the choice of the decomposition procedure for such samples are given. 

As noted already, epithermal vein-type deposits are classified primarily on the basis of their major ore-metals (Cu, Pb, Zn, Mn, Au and Ag) into the gold-silver-type and the base-metal-type. Major and accessory ore-metals from major vein-type deposits in Japan were examined in order to assess the possible differences in the metal ratios in these two types of deposits (Shikazono and Shimizu, 1992). Characteristic major ore-metals are Au, Ag, Te, Se and Cu for the Au-Ag deposits, and Pb, Zn, Mn, Cu and Ag for the base-metal deposits (Shikazono, 1986). Accessary metals are Cd, Hg, Tl, Sb and As for the Au-Ag deposits and In, Ga, Bi, As, Sb, W and Sn for the base-metal deposits (Table 1.22, Shikazono and Shimizu, 1992). Minerals containing Cu, Ag, Sb and As are common in both types of deposits. They are thus not included in Table 1.22. 

Also includes Pb, U and Th data for accessory phases allanite, leucite and aenigmatite Mineral abbreviations ... 

Michael PJ (1988) Partition coefficients for rare earth elements in mafic minerals of high silica rhyohtes the importance of accessory mineral inclusions. Geochim Cosmochim Acta 52 275-282 Mysen BO (1979) Nickel partitioning between olivine and silicate melt Henry s Law revisited. Am Mineral 64 1107-1114... 

In their study of the Laacher See eruption. Bourdon et al. (1994) obtained an isochron from their data on phonolitic pumice glasses (probably with U/Th ratios similar to those of the whole rocks) and glasses from cumulate nodules. The fractionation of U/Th ratios is attributed in that case to the crystallization of accessory U and Th-enriched phases such as sphene and apatite. The age of 14.3 6.5 ka is similar to the ages deduced from mineral isochrons (see section 3.5) and to the eruption age of 12.5 0.5 ka (Fig. 7b). Thus differentiation within the phonolitic magma occurred shortly before eruption. 

The suggestion recently made by Heumann et al. (2002) that U-Th crystallization ages in Long Valley rhyolites can reflect crystallization of accessory minerals like zircon or allanite and not of major minerals, needs to be seriously considered in other studies as... 

Further advances in the interpretation of mineral data could come from in situ analyses (unfortunately only possible presently on U-Th rich accessory minerals like zircon), or from detailed studies of particularly large phenocrysts, whose successive growth zones could be sampled (e g., through microdrillings) and analyzed. Ra measurements in such crystals could allow a direct determination of their growth rates. A systematic study of successive, well-dated eruptions of a given volcano, combining U-series measurements in both whole rocks and minerals, should also help with the interpretation of mineral data. 

Petit J-C, Langevin Y, Dran J-C (1985a) Radiation-enhanced release of uranium from accessory minerals in crystalline rocks. Geochim Cosmochim Acta 49 871-876 Petit J-C, Langevin Y, Dran J-C (1985b) " U/ U disequilibrium in natnre theoretical reassessment of the varions proposed models. Brill Mineral 108 745-753... 

Bound in minerals such as uraninite, pitchblende, coffinite, etc. fixed as a replacement ion for Y, Ce, Zr, Th, Ca, and Ba in other, particularly accessory minerals and adsorbed as ion on clay minerals, hydrous iron oxides, etc. 

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