Distribution regularities of trace elements in rocks and minerals of the ultrametamorphism zone

Abstract

The distribution of petrogenic and trace elements: Co, Ni, Cr, V, Cu, Zr, Zn, Pb, Sn, Ba, Sr, Be, Li, Rb, F, Ce, La, Nd, Y, Yb—in rocks and minerals of deep crustal horizons—in the ultrametamorphism zone— is investigated in detail for the example of the Precambrian Aldan phlogopite-bearing region. The most early formations are rocks of the granulitic facies. Their composition changes from ultra-acid to ultrabasic. Rocks of the middle and basic composition do prevail. The distribution regularities of chemical elements therein are analogous to those in rocks of younger and less metamorphosed strata. As to element content level and their ratios: Co:Ni, V:Cr, Ba:Sr, etc., there the studied stratum is found to be primary effusive-sedimentary. The ultrametamorphic transformation of the granulitic facies rocks is accompanied by an intensive loss of most trace elements and leads to a wide development of various granitoids. Lost are mafic elements: Co, Ni, Cr, Sn, Sr, etc., and granitic ones: F, Be, Li. There the forming granites have a higher alkalinity and a specific trace-element composition, e.g. alaskite has (ppm): 12.6 V, 7.0 Li, 0.6 Be, 150 F, 156 Rb, 2940 Ba, 360 Sr. Intermediate products of ultrametamorphic alteration of the basic and carbonate rocks are basificates and skarns. Therein do partially concentrate those elements lost from areas of massive granitoid development such as Ca, Mg, Fe, Co, Sn, etc., and do crystallize such minerals as phlogopite, wollastonite and spinel. Ultrametamorphism leads to formation of more contrasted rocks as to composition and trace element content than the initial ones. Rock areas enriched by a certain set of petrogenic and trace elements become a convenient medium for the formation of ore concentrations at a succeeding superposition of metasomatic processes.