ANTIMONY–MERCURY MINERALIZATION IN THE NORTHERN PART OF THE TOM–KOLYVAN FOLDED ZONE

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 exposed to a considerable extent or are covered only by a thin mantle of loose deposits, forming here the so-called Tomsk salient, which to the north plunges sharply beneath the thick loose deposits of the Ob–Chulym interfluve. East of the city of Tomsk, between two rigid blocks, i.e., the salairides of the Kuznetsk Alatau and the caledonides of the Pritomsk block, lie the hercynides of the Tom–Kolyvan folded zone.

The antimony–mercury ore occurrence is situated in the northern part of the Tom–Kolyvan folded zone.

Structurally, the area under study has a two-tiered structure. The lower, most ancient tier comprises deposits of the Upper Devonian and Lower Carboniferous and is characterized by large, strongly complicated, linearly elongated folds of northeastern trend. The structure of this structural tier is complicated by smaller folds of the second and third orders, as well as by numerous disjunctive disturbances.

Lithologically, the Upper Devonian deposits are represented by the Pachinsk and Yurginsk formations. The first is composed of clayey and marly shales, and the second of clayey and carbonaceous-clayey shales, siltstones, and interbeds of gray polymictic sandstones.

The Lower Carboniferous deposits are represented by two stages—the Tournaisian and the Visean. The Tournaisian deposits are composed of strongly pyritized clayey and carbonaceous-clayey, silt-clayey shales and siltstones with thin interbeds of sandstones and limestones. All rocks of the Tournaisian stage are calcareous to one degree or another, intensely dislocated, schistose, cut by numerous fractures, and healed by dike rocks and veinlets of quartz and calcite. The deposits of the Visean stage are represented by three formations: Lagernosadskaya, Basandaikskaya, and Kolarskaya. They are composed of clayey shales and, to a lesser extent, siltstones and sandstones.

The upper stage is separated from the lower by a significant stratigraphic hiatus, comprising loose Meso-Cenozoic deposits that have a small thickness within the Tom–Kolyvan zone.

Within the Lower Carboniferous deposits, two trends of the main disjunctive structures are outlined. One of them, the more ancient, coincides with the strike of the principal folding and is oriented in a NNE direction. The largest tectonic zone of this trend is the Kolarovo–Semiluzhenskaya tectonic crumpling zone, with which antimony–mercury mineralization is associated in the district. It can be traced from NNE to SSW for 44 km. The thickness of the zone is from 300 to 500 m. These are preliminary data; in fact, its exact extent and width have not yet been established. 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 a pinching out of this ore-bearing zone; apparently it continues to the northeast and southwest, but further investigations are needed to trace it. This zone of disturbance was first identified by M. P. Nagorskii. It is represented by zones of crushing and brecciation of rocks and consists of separate bands and sectors, some of which are composed of intensely fractured shales, while others consist of destroyed varieties of the latter—clays and ferruginized rocks with residual areas of normal shales. In places the shales are intensely silicified and penetrated by veinlets and small veins of quartz and calcite.

Antimony–mercury mineralization is confined to the large Kolarovo–Semiluzhenskaya crumpling zone. K. V. Radugin first reported the presence of major antimony mineralization in the Tomsk district in 1920. He found quartz with antimonite in the alluvium of the Kirgizka River near the village of Semiluzhki. After this, many researchers searched for the primary deposit, but no detailed prospecting work was carried out here. In 1948, A. A. Mesyaninov undertook drilling and mining work over an area of 0.002 km², which enabled him to detect antimony ores in primary occurrence in the northern part—near the village of Semiluzhki. However, A. A. Mesyaninov did not conduct detailed prospecting, but confined himself to drilling shallow boreholes on a small area of 0.002 km², as a result of which the strike of the ore bodies was lost.

In 1967 the author discovered antimony–mercury mineralization in primary occurrence in the basin of the Basandaika River; in 1968, in the basin of the Kirgizka River, as well as antimony ochres on the Kamenka River. Geologists of the Tomsk Integrated Expedition also found antimony ochres in primary outcrops on the Tom River near the village of Kolarovo. In 1969, the work of A. F. Rubtsov confirmed the presence of mineralization, exposing lens-shaped ore bodies in the area of the village of Semiluzhki.

Thus, the presence of the large Kolarovo–Semiluzhenskaya zone of tectonic disturbances of NNE strike is confirmed by antimony–mercury ore occurrences of a single genesis located along it—the Semiluzhenskoe occurrence in the north, the Basandaika occurrence in the central part, and the Kolarovo occurrence in the south. All these ore occurrences have been found in primary outcrops. In addition, in the area of the village of Zavarzino there is a deposit of radon waters. These waters, although associated with faults of northwestern strike, in general form a belt along the Kolarovo–Semiluzhenskaya crumpling zone, which has a northeastern strike. Finally, the Malkino anomaly of increased radioactivity of rocks is also confined to this same zone.

According to the author’s data, obtained during investigations here, as well as according to the work of the Tomsk Geological Expedition, in the alluvium of the B. and

Along the M. Ushaika, Basandaika, Kirgizka, Kamenka, and other rivers that cross the Kolarovo–Semiluzhenskaya fault zone, placer-prospecting has revealed antimonite and cinnabar in significant quantities.

The Kolarovo–Semiluzhenskaya fault zone is rather clearly expressed geomorphologically in the modern relief as well, being traceable by lake-like widenings of river valleys. This zone is well recorded at a number of points by drilling and also by geophysical work.

Thus, one direction of the disjunctive disturbances in the area is submeridional—north to north-northeast.

The second direction of disjunctive structures is sublatitudinal, northwestern, oriented across the strike of the main folding. These dislocations appear as zones of crushing and tectonic fractures, with which the formation of dikes of basic and subalkaline composition is associated. These dikes form linearly elongated, steeply dipping bodies 1–50 m thick. The age of the dike rocks, determined by us by the potassium–argon method, is about 245 million years, which corresponds to the Permian.