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Mineralogical Almanac  

       

Plan view of the Kazennitsa vein at the level 20 m (a) and its cross-section II-II (b).
After S.K. Borshchev.
granite pegmatite;
biotite gneiss and schist;
fine- and middle-grained biotite granite (Yuzhakov complex);
allanite porphyry granite (Vatikha complex);
loose sediments;
drillholes;
pits

 MORPHOLOGY AND STRUCTURE OF THE PEGMATITES.

Kazennitsa

                                                                          The Kazennitsa vein occurs on the right bank of the Alabashka river in 900 m to the west- northwest from the former Nizhnyaya Alabashka village and in 900 m to the east of the Mokrusha vein (see Fig. 4). The vein is of plate shape with rare flexural bends. Its length is up to 150 m, its thickness is 0.51 m, with bulges up to 23.5 m. It strikes 330340NW and dips at 4080 to the northeast. This vein occurs in biotite gneiss hosting porphyry allanite granite and biotite gneiss granite (Fig. 11). It has several apophyses forming three branches with smaller sub-branches.

The vein is asymmetrically zonal, there are three zones: (1) marginal zone (0.30.6 m) of bi- feldspar pegmatite with coarse graphic K-feldspar, up to 515 cm annite laths, and medium- graphic oligoclase replaced by spherulitic albite; (2) intermediate zone (0.20.7 m) of clearly graphic bi-feldspar pegmatite with sword-shaped siderophyllite and typical coarser graphics in the vein bulges; (3) central pegmatoid-blocky zone, with large crystals of K-feldspar, smoky quartz, and muscovite, is better developed in the southern part of the vein (up to 11.5 m) where K-feldspar crystals inside smoky quartz is up to 1.5 m, muscovite is up to 20 cm, green beryl is up to 40 cm, and also there were up to 1 m druses of rock crystal with chlorite and limonite along fractures.

Beryl crystal
(19 x 7 x 6 cm,
weight 1520 g). Kazennitsa, Alabashka pegmatite field.
Neiva GPP collection. Collected: July 1993
Photo Michael B. Leibov
 

In vein, there are small shear joints. They are either subparallel to the contacts or diagonal. Their opening is 0.53 cm, and they usually stop near the contact with vein and do not continue into more ductile host rock.

Cavities occur in the pegmatoid-blocky and graphic zones, their number is more than 200, and their size varies from first centimeters to 23 m along the vein forming up to 0.5 m wide empty space (Fig. 12). The shape of these pockets is variable from sub-isometric to chink-shaped with branches. The cavities contain druses of feldspar with quartz, muscovite, tourmaline, topaz, beryl, and other minerals (beryl and topaz are recorded in 50% of the cavities). The total length of gemstone productive part of the vein is 54 m.

Many minerals of this vein were multiply brecciated and dissolved; many of them were regenerated with regrowth of multiple heads, change of shape, and sealing of fractures. The dissolution was selective, because only one mineral was dissolved at a time or only selected facets of crystals; sometimes several minerals were dissolved simultaneously, e.g., topaz, quartz, and K-feldspar, but muscovite, albite, and tourmaline remained untouched. One of the cavities after dissolution preserved only variously shaped and colored crystals of tourmaline which have fallen on its floor. In some portions of the vein there are traces of intensive dissolution of quartz, microcline, garnet, topaz, and beryl.

In general, the sequence of mineral formation in various zones of the vein was as follows:
(a) in marginal zone orthoclase, oligoclase and albite, quartz, annite, magnetite;
(b) in intermediate zone microcline, albite, quartz, siderophyllite, almandine, schorl, beryl;
(c) in blocky zone microcline, albite, quartz, muscovite, almandine-spessartine, schorl, apatite, beryl, topaz, brookite, andalusite, gahnite, zircon, xenotime, ferrotantalite, struverite;
(d) in the cavities of the blocky zone microcline, albite, quartz, muscovite, elbaite, spessartine, topaz, brookite, andalusite, gahnite, manganotantalite, cassiterite, microlite, hematite, goethite;
(e) late minerals in the cavities muscovite, quartz, elbaite, foytite, topaz, milarite, calcite, chabazite, stellerite, rutile, fluorite, kanonerovite, pyrrhotite, sphalerite, pyrite;
(f) hypergene minerals vermiculite, montmorillonite, kaolinite, illite, goethite, psilomelane.

The Kazennitsa mine began production of beryl and aquamarine in the end of the 18th century. By 1938, it was mined down to a depth of 1014 m; after a new period of exploration works of 198791 and pilot mining in 199293 down to a depth of 30 m, it is considered to be exhausted. In fact, the 2030-m-thick vertical section of the steep-dipping Kazennitsa mine shows a wide variation of the cavity minerals which often differ in paragenesis, shape, color of minerals, sequence of crystallization, and dissolution phenomena that indicates a long functioning of the open system during formation of pegmatite. This was a first steep-dipping vein whose druse material does not exceed in beauty the lumps from Mokrusha.

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Last update: May, 5, 2007