NEW DATA ON THE GEOLOGY OF THE SARALA MINE AREA

K. V. RADUGIN

1. The area of the Sarala mine is one of two regions in the USSR where the most ancient algal flora is known, analogous to the Proterozoic flora of the Colorado Canyon in America. It has thus become one of the principal, or reference, regions where fundamental facts of the geology of Western Siberia are being established. At the same time, this area is of interest as an ancient gold mineralization, assigned by M. A. Usov to the Scandinavian phase of tectogenesis.

Thus, the geology of the Sarala ore district is of great interest. However, this geology has still been insufficiently studied. This follows in particular from our observations, which, despite their cursory character, nevertheless allowed us to establish a number of new facts.

1. Before presenting them, it is necessary to note, at least briefly, the already known ideas concerning the main features of the geological structure of the Sarala gold-ore district.

The most important among them are those set forth in the works of V. A. Obruchev, M. A. Usov, A. M. Novoselov, and P. S. Bernshtein.

The basis of the district is formed by its most ancient strata, which include the following formations: black argillaceous shales, siliceous shales, tuff sandstones, interbeds of dark fine- and fine-grained marbles, dike diabases, effusive keratophyres, felsites, and an upper suite of dark fine-grained marbles with the algonkian flora Newlandia. The above-described strata, folded into steep folds, unconformably underlie a suite of diabases, porphyrites, and albitophyres, intruded by hypabyssal granodioritic magma, with which the gold-ore mesothermal quartz veins are genetically associated. Toward the periphery the granodiorites pass into diorites and gabbro-diorites. In places within the ore field, stocks of albitites and banatites, as well as aplite-pegmatites, are also exposed.

Finally, the latest formations of the district are considered to be dikes of proterobase and the gently lying red sandstones, conglomerates, and melaphyres of the Devonian formation in the eastern part of the district. The proterobases were regarded as the roots of melaphyre lavas, but, according to A. M. Novoselov, they are considerably younger.

The tectonics of the district are complex. Their clarification is hindered by the poor development of bedrock exposures under the ubiquitous loose cover. For this reason, at present there is a fundamental difference in the understanding of the plicative structure of the ore field: according to some authors it is anticlinal, and according to others—synclinal. The direction of the folds is almost meridional. As noted above, a sharp pre-Devonian and secondary unconformity is observed in the district, in the footwall of the formation of diabases, porphyrites, and albitophyres. A very characteristic element of the tectonics of the ore field is the intersection of the quartz gold-ore veins by younger proterobase dikes, with the formation of original embryonal extension disjunctives, first established by Academician M. A. Usov.

1. The Sarala region interested me especially, first, because the geological formations of the Usinsky region and of the Usov manganese-ore deposit, which are well known to me, extend here along their strike. It is important to clarify more precisely this connection in the geology of two important regions. Secondly, the Sarala region is the first region of Siberia (and of the entire USSR) where a flora of the type of the Proterozoic flora of America (Newlandia, etc.) was discovered (initially by me). It is important to determine the relationship of the oldest deposits containing this flora to the faunistically characterized Cambrian. The solution of both problems is equivalent to establishing fundamental facts of the geology of Siberia. In 1947 I was able to spend several days in the Sarala region. The observations made at that time are set forth below.

2. Among them, in the first place, we note our find of archaeocyathids, the significance of which may prove to be very important. Unfortunately, the primary source of the limestones containing archaeocyathids has not yet been established. These limestones were found in a pile of comparatively recently mined ore (the pile had not yet become overgrown). This pile of ore (quartz) is, in volume, equal to the contents of a mine car. It was found two or three tens of meters from the cableway by which the gold-bearing quartz is delivered from the Andreevsky mine down along the Sarala. At the same time the ore pile is situated downstream from the cableway, on the left bank of Klyuch Shcheglovsky, where the old factory stood, not far from the mouth of the klyuch. The fragments of archaeocyathid-bearing pure limestone are angular. They lay on top, in the amount of several pieces, but only in one was it possible to detect a clear incomplete ring of archaeocyathids with distinctly visible septa. The color of the archaeocyathid-bearing limestone is white.

An examination of the channel of the Right Sarala below the klyuch for several kilometers revealed limestones of the same appearance, but already in the form of rounded fragments and without archaeocyathid fauna. Their roundedness cannot in this case serve as proof of a local, and not an imported, origin of the limestones, since rounded fragments of brick were also found there in the channel. However, the very idea of an imported (not from the Sarala region) origin of fragments of archaeocyathid limestone is absurd, since lime is always burned where the limestone quarries are located. Furthermore, there would have been no need to bring limestone from afar for any purpose, since it crops out not far from here at the Main Camp (limestones with the Newlandia flora).

I examined the dumps of barren rock at the Andreevsky mine itself, and there found light-colored limestones, but ones somewhat different from those containing archaeocyathids. All the same, this gives some indication of a possible source, which is completely unclear to the local geologists. Our inquiries also did not make this clear.

Another question arises: could fragments have entered the ore from beyond the main watershed, from the basin of the Middle Ters, where, as is known, V. K. Monich found archaeocyathids. But our fragments give the definite impression of freshly mined rock. Moreover, V. K. Monich’s archaeocyathid limestones are located in the backwoods, and limestone is not quarried there.

Thus, in our opinion, the archaeocyathid limestones found by us are most likely of local origin, and in the future it is necessary to find their primary source.

1. The second essential fact that we were able to establish consists in the presence, among the oldest strata of the Sarala region (above the Main Camp), of conglomerates of Cambrian or Precambrian age with fragments of altered gabbroid and other rocks. Until now the oldest intrusion of the region had been considered to be the granodiorite, which cut through all the oldest (pre-Devonian) strata of the region. Our observations

indicate the possibility of discovering an older intrusion, if, of course, it emerges at the present-day denudation surface. Incidentally, we note that in large blocks of dike diabase we found abundant xenoliths of gabbroid rocks.

1. Further, the wide development in the area of labradorite porphyries has been established; in places they apparently also produced extrusions and are genetically connected with the anorthosites. The latter were encountered by us in labradorite porphyries as large xenoliths—“messengers from the depths.”

With respect to the labradorite porphyries, the intrusive bodies of the Sarala area may be divided into two categories: younger and older. As has just been noted, there seems also to be an extrusive facies of the labradorite porphyries, representatives of which underwent marked contact alteration by the magma of the young intrusion. If this is confirmed, then the intrusions noted above, which manifested themselves before and after the labradorite porphyries, cannot be combined into a single magmatic cycle, and they will have to be regarded as two independent intrusive complexes.

1. The petrographic composition of the area is still insufficiently studied. Without citing all our observations, we shall note, in support of this opinion, the following rocks observed by us along the Right Sarala: pillowed green lavas, very reminiscent of spilite diabases; sedimentary (or tuffaceous?) breccias with fragments of felsites or albitophyres; ancient amygdalophyres (upstream from the limestone cliffs near the Main Camp), and others.

2. In the channel of the Right Sarala River we observed pebbles covered with interesting fine-grained modern deposits of a light-gray substance. We have not encountered such deposits anywhere before. They do not effervesce with hydrochloric acid. In our opinion, these are chemical deposits formed after the appearance of the Sarala ore deposit. Of the same age are pebbles of slag, brick, cement, some snow-white porphyroid material, and coal. Of interest is the good roundness of the brick pebbles, despite the short distance traveled by the pebbles (no more than 2–3 km), and the process of rounding, very brief in comparison with geological time.

3. Thus, we have noted new and fairly substantial details of so interesting and important a geological area as the Sarala area. They already possess a certain value. In addition, they emphasize the still insufficient study of the geology of the Sarala area, which serves as a reference point in certain major questions of the geology of Siberia. It is therefore necessary to hope that, in the near future, the gaps in geological knowledge of it will be filled.