Other
Scientific paper
Feb 1963
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1963gecoa..27..155g&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 27, Issue 2, pp.155-181
Other
7
Scientific paper
The numerous small (1-3 ) gaseous and liquid inclusions in granite minerals were extracted from the samples by grinding in vacuum at normal temperature. This procedure is quantitative, contrary to the separation by decrepitation at high temperatures and also avoids the higher possibility of reactions inherent to the latter method. A description is given of the vacuum ball-mill that grinds the mineral particles (grain size: 1-2 mm) in a closed and evacuated container. The ball-mill and the balls show no noticeable gas development. This was tested by trial runs with optically pure quartz. In the course of the development of this procedure, the origin of the large amounts of nitrogen (up to 1 ml NTP/g mineral) found in former gas-extracts from minerals ground in vacuum ( 1949 and 1956) was cleared. Samples of 0.5 to 1 g are sufficient for this method of extraction in combination with a vacuum-apparatus of the type used by Wahler (1955) for the determination of partial pressures. The samples were taken from four postorogenetic hercynian granites and their pegmatites, from the Black Forest and the Vosges. Their inclusions could be expected to be mainly of primary origin. Furthermore two other granites, a pegmatite, two samples of olivine from nodules in basalt and a cyanite were examined. The following amounts of gases (in mm 3 NTP/g) were found in the minerals of the young granites: H 2 10-150, CO 2 0-40, CO 0-4, N 2 1-8 and in the minerals of the pegmatites: H 2 2-60, CO 2 0-20, CO 0-2, N 2 1-9, CH 4 0-2, C 2 H 6 traces. The amounts in the olivines were noticeably lower. It was found that most of the hydrogen, at any rate in biotite, is not contained in inclusions but dissolved in the mineral. A critical discussion of the results of former CO 2 determinations, together with own experimental data, shows that the large amounts of CO 2 found by and (1956) and most of those found in this investigation originate from carbonates. It is shown that traces of carbonates in samples of hard silicate minerals are mostly decomposed not only by heating but also by grinding in vacuum. Thus, no known method is accurate in the selective analysis of free carbon dioxide in small inclusions. The experiments demonstrate that carbon monoxide also is generated from carbonates in amounts comparable to the total amounts found. Thus, the above values for free CO 2 and CO are upper limits. The actual amounts can be lower by magnitudes. It was found that CO 2 in the examined granite quartzes is mainly bound to Ca in carbonates. The water contents in the inclusions of all the samples were also determined in the vaccuum apparatus (10-6300 mm 3 NTP/g). The dissolved chloride and sulfate anions were determined chemically. The dissolved cations K + , Na + and Ca ++ were also determined in most of the granite and pegmatite quartzes, in the olivines and in the sample of cyanite. The main and definite components of the inclusions in most of the examined granites and pegmatites are a quite concentrated solution of salts and nitrogen as gaseous phase.
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