Влодавец, В. И. Нефелино-апатитовые месторождения в Хибинских

It appears as if apatite, along with the smashed mass of other mine­ rals, was intruded into the urtite-rock. The alkaline basal rocks of the ijolite-urtite series are remarkable for higher contents of apatite. The literary evidence, as well as the field and microscopic observa­ tions over nepheline-apatite and adjacent rocks, led the writer to follo­ wing conclusions as to their genesis. The apatite matter separated and concentrated from the ijolite-urtite magma, forming a kind of apatite magma. Thanks to its origin from the ijolite-urtite magma, it necessarily contained, in addition to nepheline also the components of the mother- inagma. The apatite magma, appearingly thanks to sudden sharp lowering of pression, assumed a progressive motion and crystallized without being definitely separated from the mother-magma at the boundary between ijolite-urtites and nepheline-syenites. Thus originated a quite peculiar nepheline-apatite rock consisting mainly of apatite and nepheline and of a little amount of secondary minerals, such as aegirine, alkaline hornblende, titanite and titanomagnetite. Studying that rock from the hanging flank towards the lying one, it was seen that the whole zone adjacent to the upper margin is very rich in fine-grained, sugar-like apatite (microphotograph 1 0 ) with little spots of nepheline (microphotograph 11)—( s p o t t e d zone). This first zone is gradually passing into the second, also j 4 ^ch *in alike apatite, which however, besides single spots of other minerals, contains bands of the same ( s p o t t y - s t r i a t e d zone). T h e ^ e c o n d zone is giving way, also gradually, to a zone with a rock less rich in apatite, where stranger minerals form dark bands ( s t r i a t e d zone). Such constitution and mineralogical composition of the rock are d is­ tinctly observed along the trend and across it. As to the amount of principal constituents in the rock, gradual tran ­ sition is observed from rich zones with apatite contents up to 80%, to poor ones with about 2 0 % of apatite. Inverse conditions are being obser­ ved with nepheline; i. e. its amount is growing from the upper horizons downwards, reaching 80% at the lying flank. In Table I the analysis is given of a rock rich in apatite (1) from the upper zone and poor in apatite (II) from the lower zone. Table 2 shows the analysis of the coarse grained apatite from the middle zone. Table 3 contains the chemical analysis of nepheline. The analyses reveal some interesting items, such as 1) the presence of rare earths and in particular of considerable amount of strontium; 2 ) the increasing con ten ts of rare earths, strontium, fluor from lower horizons upwards, and 3) the changing composition of apatite, which is fluor-apatite in the upper horizon and fluor-chlor-apatite in the lower. The nepheline-apatite rock from the upper horizon with spotted or spotty-striated structure contains 60 to 80% of apatite, 15—35% of ne ­ pheline and about 5% of aegirine, arfvedsonite, biotite, sphene and ore mineral, whereas that from the lower horizon contains 20—50% of apatite, 59