Gold from the Tomsk Area

A. F. Korobeinikov, B. V. Plotnikov, A. M. Kuzmin

The first information about gold in the environs of the city of Tomsk became known at the end of the last century. Brief references to this can be found in the works of A. M. Zaitsev [3], V. S. Reutovsky [5], V. A. Obruchev [6], I. P. Bersenevich [1], A. M. Kuzmin [4], and A. Ya. Bulynnikov [2]. Despite finds of primary and placer gold, no special prospecting-and-evaluation work for gold was carried out in the Tomsk area. Therefore, the degree of gold content of the various hydrothermal formations of the area and the nature of the primary and placer gold remained unclear.

In connection with this, in 1969, with the active participation of students of the Geological Prospecting Faculty of TPI, one of the authors of the article carried out heavy-mineral sampling work in the modern channel deposits of the rivers Ushaika, Basandaika, and Malaya Kirgizka in the estuarine parts of their valleys. The washing of samples was carried out with pans and on a rocker.

Before presenting the characteristics of the morphology of the gold particles obtained from the placers, we shall note certain features of the gold content of the structural-facies zones of the region. Gold is found in two structural tiers of the region. The first structural tier is composed of shales and sandstones of Lower Carboniferous age. They are gathered into steep folds of northeastern strike, are cut and metamorphosed by diabase dikes and quartz veins, with which, in the opinion of A. M. Zaitsev [3] and A. M. Kuzmin [4], the gold mineralization is associated.

M. P. Nagorsky notes that gold particles are found in ancient placers of Meso-Cenozoic age, consisting of loose sandy-clayey, weakly metamorphosed sediments of the second structural tier.

Most often gold occurs in the channel alluvium of the small rivers Ushaika, Basandaika, Tugoyakovka, and Kirgizka, as was noted in the works of A. M. Zaitsev, V. A. Obruchev, and others.

On the question of genetic links between primary gold and the sources of gold in the young and ancient placers of the area, information is available only in the articles of A. M. Kuzmin [4] and A. Ya. Bulynnikov [2]. They believe that the gold is associated with quartz veins that cut the Paleozoic rocks of the region. A. Ya. Bulynnikov allows for the possibility of a genetic connection between the gold mineralization and diabase dikes, and considers ancient placers to be the source of the modern placers.

A. M. Kuzmin’s work, carried out in 1944–1945 for the purpose of studying the mineralogical composition of quartz veins, showed that there exist—

Fig. 1. Morphology of gold from placers of the Tomsk area:
a, d, e, zh — petal-like form of gold particles with bent edges;
b — thick-tabular gold particle intergrown with oxidized pyrite (2);
v, z — petal-like gold particles intergrown with pyrite (2) and quartz (3);
g — thick-tabular gold particle intergrown with quartz (3).

there are two generations of quartz veins. Of these, only those quartz veins whose strike coincides with the dip of the schistosity of the Paleozoic rocks proved to be auriferous. The quartz veins of the second generation, which cut the diabases, carry mercury–stibnite mineralization.

The study of the mineralogical composition of heavy-mineral concentrates from the placers of the Ushaika, Basandaika, Tugoyakovka, and Kirgizka rivers showed that pyrite and chalcopyrite grains, oxidized to varying degrees, magnetite, and rare small gold particles are most often found in the heavy fraction. A dependence of the concentrate composition on the composition of the sediments cut by the streams was noted: where the streams flow through loose Paleogene–Neogene sediments, gold is absent from the concentrate, as is the case in the near-mouth part of the Malaya Kirgizka River. Conversely, in places where the stream channels are incised into Paleozoic rocks of the lower structural stage with diabase dikes and quartz veins, small gold particles appear in the concentrates.

Microscopic studies of the gold particles showed that their size ranges from 0.6 to 0.03 mm. The shape of the gold particles is mostly thin-platy, often petal-like with bent edges (Fig. 1). The gold particles occur in intergrowths with oxidized pyrite. The pyrite is replaced by goethite with preservation of the cubic form of the primary pyrite and with relict striation parallel to the cube edges. In addition to cubic forms, pentagonal-dodecahedral forms of oxidized pyrite 0.04–0.08 mm in size are also encountered occasionally.

Individual thick-tabular and petal-like gold particles occur in intergrowth with long-prismatic semitransparent quartz crystals and pyrite (Fig. 1). In addition, vein-like gold particles have been found in a quartz vein exposed in sandy-shaly rocks of Upper Carboniferous age on the Ushaika River near Tolstyi Cape, 150 meters upstream from the stone bridge.

Thus, on the basis of the study of the morphology of gold particles from placers in the vicinity of the city of Tomsk, the following conclusions may be drawn:

1. Gold is associated with the formation of quartz veins containing pyrite, chalcopyrite, arsenopyrite, sphalerite, and galena and cutting Paleozoic sandy-shaly rocks. Auriferous quartz is found among diabase dikes, which are most often accompanied by their own quartz veinlets with carbonates and antimonite.

2. The gold particles filled the intergranular spaces of drusy cavities and the finest cracks in the quartz veins together with pyrite and chalcopyrite. The shape of the gold particles is most often platy and petal-like; their size is 0.6–0.03 mm. Gold crystals are exceptionally rare and are represented by the cube and octahedron.

3. Gold was deposited later than pyrite and chalcopyrite, since phenomena of sulfide encrustation by gold are constantly observed.

4. The placers probably formed from relatively nearby sources, since intergrowths of oxidized pyrite and quartz are constantly noted in the gold particles, i.e., complete separation of gold from the accompanying minerals has not yet occurred.

Consequently, in studying the mineralized zones among the Paleozoic formations of the region, and first of all the silicification zones, prospecting work for gold should be carried out.

REFERENCES

1. Bersenevich I. P. Report on statistical-economic studies of the Tomsk Mining District. Petersburg, 1912.

2. Bulynnikov A. Ya. Questions of the gold content of the environs of the city of Tomsk. In collection:

“Materials on the Mineralogy, Petrography, and Mineral Resources of Western Siberia.” Tomsk University Press, 1962.

1. Zaitsev A. M. Geological investigations along the route of the Siberian Railway. Vol. 5. St. Petersburg, 1896.

2. Kuzmin A. M. Upper Paleozoic gold mineralization in the environs of the city of Tomsk. “Geology of Ore Deposits,” 1961, No. 2.

3. Reutovsky V. S. Mineral Resources of Siberia. Part 1. St. Petersburg, 1905.

4. Obruchev V. A. Geological survey of the gold-bearing regions of Siberia. Issue 1, “Western Siberia,” St. Petersburg, 1911.