Volume 11, pages 289-299, 1926

      Our experience has been that every new journey to this field develops new mineralogical discoveries since a large number of gorges and portions of plateaus have not yet been visited. The study of this material is still being pursued by numerous workers in the Mineralogical Museum; new facts are being discovered, so that our knowledge of these massives is far from being complete.¹

      GENETIC HISTORY. The regular distribution of genetic types is connected with the mode of origin and method of cooling of these magmatic masses. As yet the studies have not been completed, and one must construct hypotheses for the explanation of the observed correlations.

      Careful study of the course of the geological processes of Hibina-Toundra show two very marked periods in the history of the mineralogical events. The first period separates the magmatic and pegmatitic stages, which in all cases was marked by the formation of immense radiated masses of aegirite of the second generation. At this time the earlier formed magmatic minerals became unstable: aenigmatite was replaced by astrophyllite, elatolite was removed, the stream of volatile elements increased, and the formation of minerals of lower specific gravity began.

      This was due not so much to the variation of temperature as to the unexpected lowering of pressure. This type of phenomena was especially characteristic of the central zone of Hibina, where we undoubtedly have to deal with the region in which the formation of the minerals proceeded under decreased pressure.

      The second period in the geochemical history of the massive was determined by the Equation of the steam (about 300-400°C). From then on appeared the typical hydrothermal veins (zeolites).

      It is more difficult to trace the genetic processes in Lujavr-urt, as this Toundra has not been sufficiently studied. Nevertheless, one is attracted by the great resemblance of the lujavritic pegmatites with the contact zones of Hibina Toundra.

      MINERALS PRESENT

      About ninety minerals have been found in the nepheline syenites and their endocontact zones. These are listed below. Those identified only under the microscope are placed in parentheses, while the more interesting ones are given in italics.

      SULFIDES (6): chalcopyrite, galena,  molybdenite, pyrite, pyrrhotite, sphalerite.

      HALOIDS (2): fluorite, yttrocerite.

      CARBONATES (4): calcite, calcioancylite, elatolite, malachite. 

      PHOSPHATES (1): cerium apatite.

      OXIDES (15): agate, (anatase) chalcedony, (corundum), flint, (hydrargyllite), ice, ilmenite limonite, manganese oxides, quartz, (quartzite), (rutile), (spinel), zircon. 

      SILICATES (45): actinolite aegirite, (aegirite-augite), (albite), analcite, (andalusite), (andesine), anornite, anorthoclase, arfvedsonite, barkevikite, biotite, cancrinite, cataforite, chabazite, chlorite, chrysocolla, (diopside), epidote, epistilbite(?), (garnet), hackmannite, hastingsite, heulandite, hornblende, hydronephelite, kaolinite, mesolite, microcline, natrolite, nephelite, nosean(?), olivine, orthoclase, pectolite, pyroxene-titaniferous, schizolite, (serpentine), (sillimanite), sodalite, taeniolite, thomsonite, ussingite, (wollastonite), yuksporite.

      ZIRCONO-TITANO-SILICATES (15): Eudialyte group: aenigmatite, astrophyllite, eucolite, eudialyte, låvenite, lamprophyllite, lovchorrite, mangan-neptunite, mesodialyte, murmanite, ramsayite, rinkolite, rosenbuschite, titano-elpidite, wöhlerite.

      TITANATES AND TANTALATES (4): loparite, perovskite(?), (pyrochlorite ?), sphene.

      DESCRIPTIONS

      AENIGMATITE. This is very common in several types of segregation veins, forming large irregular crystals weighing several kilograms. It is accompanied by aegirite, microcline, nephelite, and eudialyte. Astrophyllite and aegirite when bordering this mineral, sometimes replace it entirely, forming a variety of reaction-rim called coronite.

      ASTROPIIYLLITE. Likewise very common in large golden-yellow plates, or fine filiform and fibrous masses, associated in the latter form with pectolite, sphene, and natrolite. Masses weighing ten kilograms were found.

      CALCIO-ANCYLITE. This mineral is similar to ancylite from Narsarsuk, Greenland, in its crystallographic and physical properties. It occurs in small yellow, tinged with gray or brown, crystals, coating the cavities of an unidentified mineral, associated with zircon, natrolite, ilmenite, acicular aegirite, and occasionally with small quantities of yttrocerite.

      CERIUM-APATITE. Green apatite is rather common in nephelite syenite veins in masses of probably commercial importance. It contains about 3.18% of the rare earths of the cerium group. It occurs associated with magnetite, nephelite, biotite, aegirite, sphene, and microcline.

      ELATOLITE. Under this name, A. E. Fersman has described traces of a mineral filling cavities about 8 cm. in length with an arborescent crystalline skeleton. Crystallographic examination indicates an origin from primary calcium carbonate stable at a temperature above 1000°C, and disappearing entirely at a decreased pressure.

      EUDIALYTE GROUP. In variety of color and abundance of crystal forms, the members of the eudialyte group have proved exceedingly interesting. It is found sometimes in large masses. There are many types, from violet-red eudialyte to the brown eucolite. The change of color follows the increase in specific gravity, increase of rare earth content, and gradual change of optical sign ( + to -), with the intervening pseudo-isotropic variety called mesodialyte.

      HACKMANNITE. Common in Lujavr-urt, associated with sodalite. It has a violet-red tinge on a fresh fracture, which rapidly disappears after a few minutes exposure in the open air.

      LAMPROPHYLLITE GROUP. Lamprophyllite is one of the most remarkable of the Hibina and Lujavr-urt minerals. It occurs in poorly developed crystals up to 20 cm. in length, or in stellate groups, with a perfect cleavage, and a semimetallic luster. Its exterior resemblance to astrophyllite is very striking so that it is very difficult to distinguish them without testing. It occurs associated with eudialyte, aegirite, and rinkolite. The mutual replacement of zirconium by titanium, and CaO by SrO and BaO is characteristic, with corresponding variations in optical properties.

      LOPARITE. It is a black mineral, with a metallic luster, forming pseudocubic penetration twins. The principal forms are (100) and (111). It occurs in umptekite along the line of contact associated with eudialyte, aegirite, ramsayite, and sphene.

      MANGAN-NEPTUNITE. This mineral was found locally in the contact zone of the Hibina massive, in dark red, almost black crystals, associated with fibrous aegirite, natrolite, and analcite. It occurs also in the pegmatites in the lujavrite of Lujavr-urt, associated with aegirite, natrolite, eucolite, and ramsayite.

      MURMANITE. This is a violet, scaly mineral with a perfect micaceous cleavage, and a semimetallic luster, occurring both in Hibina-Toundra (rare), and in Lujavr-urt (in beautiful plates of considerable size).

      PECTOLITE. It occurs in large masses in gneissic pegmatites or nephelite syenites. Numerous analyses show it to possess a variable composition. It is accompanied by sphene, fibrous astrophyllite, aegirite, biotite, natrolite, and more rarely by grains of fluorite, galena, and sphalerite.

      RAMSAYITE. It differs from lorenzenite in the absence of zirconium. It occurs as large, dark brown, well developed orthorhombic crystals up to 3 cm. in length. It is associated with feldspar, nephelite, aegirite, and eucolite. It has been prepared artificially.

      RINKOLITE. It is very common in the Hibina-Toundra, forming elongated and lamellar crystals of yellowish-green color, which may attain a length of 20 cm. At one locality, large brown, colloidal masses weighing hundreds of kilograms were found (lovchorrite). It is related to mosandrite and rinkite, resembling the latter in paragenesis and exterior appearance.

      SCHIZOLITE. This mineral is very rare, and occurs only in ussingite in single crystals.

      TAENIOLITE. It occurs in laminae resembling the mineral from Narsarsuk, Greenland, and was found in the valley of Mannepahk in Hibina-Toundra, in the contact zone.

      TITANO-ELPIDITE. It occurs in small quantities in the contact zone associated with albite and the oxides of manganese. It differs from elpidite from Narsarsuk, Greenland, in having titanium prevailing over zirconium, with corresponding differences in optical properties.

      USSINGITE. It was found in a boulder in Lujavr-urt with aegirite and schizolite. Its composition and properties are identical with the mineral from Kangerdluarsuk, Greenland.

      YUKSPORITE. It is a pink lamellar, or scaly mineral, which appears to be a member of the pectolite group, but contains more sodium. It is found intergrown with sphene, and accompanying pectolite, astrophyllite, biotite, and aegirite.

      GEOCHEMISTRY

      From the geochemical standpoint the massives are of great interest because of their characteristic elements. The table below lists these in order of decreasing importance. The prevailing elements which determine the type of geochemical province are printed in heavy type:

      (I) O, F, Na, Mg, Al, Si, P, Cl, K, Ca, Ti, Mn, Fe, Zr, Ce group. 

      (II) H, C, S, Cu, Mo, Pb, Zn, Sr, Ba 

      (III) V, Y, Nb, Hf, Ta, Th, Li (Au?)

      The elements of the middle atomic weight strikingly predominate, and the absence of light volatile metalloids and heavy metals is also marked. Even numbered elements, especially those of the fourth periodic group, prevail. Compared with other great alkaline regions the following features are noteworthy: the predominance of titanium over zirconium (as it is in Greenland and the Langesundfiord); and the prominence of phosphorus, the cerium group of rare earths, strontium and barium.

      While the geochemistry and mineralogy of the contact zones resemble the assemblages of Narsarsuk, Greenland, the central part of Hibina-Toundra more nearly approaches the dikes of alkaline rocks in that country. The minerals of Lujavr-urt, however, somewhat resemble those of Pilandsberg in South Africa. Without analogy, and quite exceptional, are the ramsayite pegmatites of Lujavr-urt, in which are to be found assemblages of rare beauty consisting of hackmannite, elatolite, lamprophyllite, ramsayite, eucolite, and murmanite - six of the characteristic minerals of the Kola Peninsula.

      Tables II and III summarize some of the more important chemical analyses, physical and optical properties of a number of the minerals of this region.

      TABLE II. SELECTED ANALYSES OF SOME OF THE MINERALS FROM HIBINA-AND  LUJAVR-TOUNDRA

 NOTE

      1 About fifty papers have been published in various journals on special investigations of the Expeditions. The general summary appears in three volumes: the first, with a map of Lujavr-urt and the routes appeared in 1925. The second volume, to appear in 1926, will contain the geological and petrographical results, with a description of the localities. The third volume will describe the mineralogy and geochemistry of the massives.