APATITES FROM PLUTONIC IGNEOUS ROCKS OF THE ALDAN SHIELD

Abstract

In metallogenic studies, it often is necessary to find the source of ore material in order to model the genesis of ore associations. For the Aldan apatite province, we shall consider what possibilities there are for identifying the sources of apatite ores that belong to different associations. On the basis of the types of source material, we can identify three model forms of apatite that crystallized in the mantle and at the levels of the basaltic and granitic crustal layers, respectively. Seligdar-type apatites are similar in content of SrO, Cl, ΣREO and SO3 to apatites that crystallized at the basaltic-layer level. They are closest to apatites from deep-seated xenoliths of gabbro-anorthosite diaphthorized under amphibolite-facies conditions. The strontium-isotope ratios in Seligdar-type apatites range from 0.7039 to 0.708, being lowest (≤0.7065 [sic]) in magmatic varieties and highest in metasomatic. Such apatites probably developed when material was introduced from the mantle and basaltic-layer levels. The above data show that direct mineralogic evidence confirms assumptions about the phosphorus specialization of mantle and basaltic-layer levels beneath the Aldan shield in zones of Mesozoic igneous activity.