ANTIMONY–MERCURY MINERALIZATION

IN THE SOUTHERN PART OF TOMSK OBLAST

G. M. IVANOVA

(Presented by the scientific seminar of the Department of Petrography)

The rocks of the Paleozoic basement in the south of Tomsk Oblast are, to a considerable degree, exposed or are covered only by a thin mantle of loose deposits, forming here the so-called Tomsk salient.

Antimony–mercury ore occurrences in Tomsk Oblast have been found within the Tomsk salient, in the northern part of the Tom–Kolyvan folded zone, and are confined to the large Kolarovo–Semiluzhki zone of deformation of NNE strike.

K. V. Radugin was the first to report the presence of antimony mineralization in the area of the city of Tomsk in 1920, having discovered quartz with antimonite in the alluvium of the Kirgizka River. In 1948, A. A. Mesyaninov undertook drilling of shallow boreholes on a small site, which enabled him to identify antimony ores in bedrock near the village of Semiluzhki. However, in 1967 we discovered antimony–mercury mineralization in bedrock in the basin of the Basandaika River, 1.5 km upstream from the village of Anikino (an area south of the village of Semiluzhki by 20 km). Later, in 1968, in the basin of the Kirgizka River, 1.8 km upstream from the mouth of the Kamenka River, we found dumps of antimonite, and on the Kamenka River (1.2 km upstream from the mouth)—a quartz vein with antimony ochers. Drilling operations carried out in 1968–69 by M. P. Nagorskii, N. V. Grigor’ev, and A. F. Rubtsov confirmed the presence of antimonite ore bodies on the Kirgizka River. In addition, geologists of the Tomsk Integrated Expedition also discovered antimony ochers on the Tom River near the village of Kolarovo.

A careful heavy-mineral survey carried out by us in 1968 in the area of the Semiluzhki ore occurrence made it possible to distinguish here three most promising sites (the Kamenka–Mezhovka Rivers site; the Malka River site; and the Kirgizka River site). A metallometric survey, carried out by us in 1969–1970 along outcrops and by the probe method on a 15 × 20 m grid in the promising areas of the Semiluzhki ore occurrence, confirmed the contamination of the area with antimony and mercury.

In the ore occurrences mentioned above, the ore minerals encountered include pyrite, pyrrhotite, magnetite, sphalerite, galena, chalcopyrite, gold, antimonite, and cinnabar; among the non-ore minerals—quartz and calcite.

The sequence of Lower Carboniferous deposits of submeridional strike, which in all probability is ore-localizing, is cut by a number of disjunctive disturbances of various trends, mainly submeridional and sublatitudinal. These two systems are developed to an unequal degree, the sublatitudinal ones being the most developed. The sublatitudinal fractures are transverse with respect to

strike of the folded structures of the district and are rupture fractures. Dolerite-diabase dikes of this composition, widespread in the district, are confined to these fractures, as is rather varied mineralization in quartz and quartz-carbonate veins and directly in the dikes. Among the veins of sublatitudinal strike there are practically barren ones without mineralization, as well as those with a fairly abundant dissemination of pyrrhotite, pyrite, less commonly chalcopyrite, sphalerite, and magnetite. The sublatitudinal fractures are the earliest in comparison with the submeridional ones. The submeridional fractures are associated with a fault zone of analogous strike, extending in the direction Semiluzhki—Basandaika—Kolarovo and farther south, and also north of Semiluzhki. Quartz and quartz-carbonate veins are also associated with this system of fractures; in some cases they are barren, in others they contain abundant mineralization. The character of the mineralization here differs substantially from that in fractures of the first type: namely, the most interesting antimony-mercury mineralization appears, represented by cinnabar and antimonite. Other sulfides in these veins are fairly rare—pyrite, chalcopyrite, and, less reliably, galena and sphalerite are observed in small quantities.

Thus, proceeding from the presence of two systems of fractures with different mineral associations, two stages of mineralization may be distinguished. The first—the earliest—is associated with sublatitudinal fractures—

Table 1

... and proceeded immediately after the intrusion of dikes; the second—later—stage is confined to major faults of submeridional strike. It no longer has a direct spatial connection with the dikes, but probably appeared under the influence of deep-seated solutions that penetrated along zones of faults of submeridional trend. The second stage of mineralization was most active at the nodes where fractures of the first and second types intersect.

The hypogene mineralization of the first stage is usually finely disseminated; accumulations of pyrrhotite and pyrite are observed more rarely. Individual minerals are often separated in space. The earliest of the sulfides is pyrrhotite; pyrite develops somewhat later, and then chalcopyrite, replacing pyrite. Emulsion disseminations of sphalerite are often observed in chalcopyrite. Outside chalcopyrite, sphalerite is also represented by fine disseminations. Galena is also observed in small amounts in the form of individual grains. Gold is deposited last. Individual grains of it, measuring hundredths of a millimeter, are observed. Very often, secondary quartz, disseminated pyrite and chalcopyrite are observed within the dikes themselves, and disseminated sphalerite in the selvages. This testifies to the genetic relationship of mineralization of the first type with the dikes and to a common source of supply (Table 1).

The general distinguishing feature of the second stage, as compared with the first, is the presence of cinnabar and antimonite and the scarcity of other sulfides. The second stage is, on the whole, lower-temperature and is characterized by a poorer gold content.

The Kolarovo–Semiluzhki folded zone, which carries antimony–mercury ore occurrences, is reflected fairly well in the modern relief geomorphologically, as well as in outcrops, by drilling and by geophysical work. This ore-bearing zone is traced from NNE to SSW for 44 km. Its thickness is approximately from 300 to 500 m. At the same time, we have no grounds to assert that the distribution of mineralization is limited to this; on the contrary, we see no signs indicating the pinching out of this ore-bearing zone. Apparently, it continues to the NN and SSW, but further investigations are necessary in order to trace it, and also to discover blind ore bodies associated with it.