On distinguishing quartz of hydrothermal or metamorphogenic origin in different monomineralic veins in the eastern part of Germany

Abstract

Investigations were made on quartz veins in rocks of the crystalline basement of the German regions Sachsen, Thuringen and Harz Mountains in the former GDR characterizing them genetically for industrial purposes. Fluid inclusions show differences in frequency, size, shape and filling degree between hydrothermal and metamorphic quartz. Homogenization temperatures range from 200 to more than 300°C for metamorphic quartz and from about 100 to more than 250°C for hydrothermal quartz. Pressure corrected homogenization temperatures of metamorphic quartz fluid inclusions exceed 500°C but are available only for this type. Pressures determined for metamorphic quartzes range from 120 to more than 300 MPa. Cryometrically analysed salinity varies from relatively low values (about 10 equiv.-% NaCl) for metamorphic quartz to widely scattered values (8 to 26 equiv.-% NaCl) for the hydrothermal type. The results agree well with the composition of the occluded solutions determined by chemical analysis which range from 20 to 160 g/l for metamorphic quartz, and from 50 and more than 300 g/l for hydrothermal quartz. Chemistry of the metamorphic quartz inclusions is dominated by Na, Cl and HCO3 ions, whereas Ca ions prevail in hydrothermal quartz. Some of the properties found are important for the melting behaviour of quartz in glass production.