On the geochemistry of postsedimentary mineral formation in the Tremadoc graptolitic argillites of North Estonia

Authigenous minerals occur in graptolithic argillites, more exactly in aleurite intercalations, as individual crystals forming cement and concretions. Silicic, carbonate and sulphide minerals are most widespread of the argillites. At ·the early stage of diagenesis organic compounds and clay minerals adsorbed from mud solutions rare and dispersed elements, in particular molybdenum and vanadium. Postsedimentary, carbonate and silicic formations did not consolidate vanadium and molybdenum. Тhе degree of consolidation of the former carbonate concretions compared with graptolithic argillite гanges from 0.03 to 0.2 and from 0.03 to 0.1 respectively and in silicic formations from 0.2 to 0.3 and from 0.2 to 0.6 respectively. Consolidation of molybdenum proceeded only in sulphide postsedimentary minerals (chiefly pyrite). The molybdenum content in pyrite ranges between 5.6 • 10-4 and 1.5 • 10-2 % (the degree of consolidation of molybdenum compared with argillite rages to 7.5). The vanadium content in pyrite is small ranging between 5 • 10-3 and 1 • 10-30 % (the degree of consolidation varies between 0.03 and 0.1).