Home – Home – Jornals – Russian Geology and Geophysics 2003 number 12

The Late Paleozoic-Early Mesozoic Erdenetiyn-Ovoo magmatic center in Northern Mongolia includes the plutonic Selenge and subvolcanic ore-bearing porphyry complexes different in age and emplacement conditions but similar in major-element chemistry (calc-alkaline patterns, higher alkalinity, Na enrichment over K, etc.) and initial ⁸⁷Sr/⁸⁶86Sr ratios (about 0.7039-0.7044). Over 300 chemical analyses processed by correlation, cluster, and factor analysis techniques demonstrate general similarity and features of difference in the Selenge and porphyry complexes. Some element abundances in rocks of the same type in the compared complexes show different distribution functions. Correlation and cluster analysis reveal weaker linkage among elements in porphyry than in the Selenge granitoids. The composition of the Selenge complex in factor diagrams bears a stronger effect of differentiation and alkalinity, and porphyry magmatism, especially the ore-producing late phases, was also controlled by oxidation state. The weaker role of alkalinity in porphyry may be accounted for by loss of alkalis during separation of fluids from the magma. The general and specific features of major-element chemistry indicate that the Selenge and porphyry complexes originated at different stages of a single long-existing magma system of deep origin in which the conditions were favorable for concentration of ore components in late melts.