Ein Beitrag zur Geochemie des Schwefels

Abstract

Two chemical methods for the determination of small quantities of total and sulphide sulphur in silicate minerals and rocks are described. Sulphate sulphur, in general, is obtained as different from total and sulphide sulphur. The determination of sulphur contents down to 0·002 per cent is possible. The mean deviation lies for contents below 0·02 per cent at ±0·001 per cent; for contents between 0·02 and 0·1 per cent at ±0·0015 per cent. Ninety-six mineral and 132 rock samples were analysed. In nearly all of them, total sulphide and sulphate sulphur were determined. The mineral analyses indicate that many rock-forming minerals contain small quantities of sulphate sulphur. In quartz up to 0·0095 per cent, in feldspars 0·022 per cent, in muscovites 0·013 per cent, in pyroxenes 0·007 per cent and in various sorosilicates up to 0·014 per cent sulphate sulphur was found. The average total sulphur content of each mean family of igneous rocks is nearly 0-03 per cent S. The alkali rocks usually show higher contents. Sulphur occurs in igneous rocks both as sulphide and sulphate. In gabbros the sulphate portion, when present, is very small. On the average, plutonic rocks contain more sulphide sulphur and less sulphate sulphur than their effusive equivalents; silicic rocks contain less sulphide sulphur than basic rocks. The percentage of the total sulphur that is sulphate sulphur is higher in silicic rocks than in basic rocks. For three granites and one basalt, it could be shown that the feldspars are preferred hosts for sulphate sulphur. Several possibilities for the mode of sulphate sulphur in igneous rocks are discussed. From leaching studies it seems probable that sulphate in silicate minerals appears not only in fluid inclusions, but that also replacement of SiO 4 by SO 4 in the silicate, may occur. In sedimentary rocks the sulphur is found both as sulphide and sulphate; mainly as sulphide in shales, (average: 0·22 per cent S), in greywackes, (average; 0·13 per cent S) and carbonate rocks, (average: 0·12 per cent S), and as sulphate in sandstones, (average: 0·022 per cent S) and pelagic sediments, (average: 0·13 per cent S). Metamorphous rocks also contain sulphide and sulphate sulphur. Calculations indicate that the total sulphur contents of the oceans, of the common sedimentary rocks, and of the evaporite deposits of the earth, are almost alike, and that the sulphur in these must to a great extent have originated from degassing magmas.