On the Gold Potential of Magnetite Deposits in the Altai-Sayan Mountain Region

A. Ya. Bulylnikov (TSU)

It must be acknowledged that in the instructional literature on ore deposits there are extremely scant data on the gold potential of magnetite deposits, in particular those of industrial value. Thus, in the well-known textbook by K. I. Bogdanovich [2], only the Vorontsov iron-ore deposit, located in the group of the Bogoslovsk copper-ore deposits of the Urals, is noted. In the description of the Vorontsov deposit it is stated that the iron ores, in the form of magnetite and predominantly martite, form large and small accumulations in augite-garnet rocks (skarns). In such rocks quartz is also often present in the form of nests and veinlets. The gold content in the quartz was in places very high. The iron ores of the deposit are rich in manganese.

In Siberia, even before the revolution, Ya. S. Edelstein, during geological investigations in the south of Krasnoyarsk Krai, noted the presence of gold in silicified magnetites of the Kaliostrov deposit. The latter is located in the system of the White Iyus of the Kuznetsk Alatau, within the Kommunar ore field. Later it was studied and described by A. Ya. Bulylnikov [3]. The deposit is confined to garnet-pyroxene skarns of the contact zone of a small intrusion of augite diorites of Lower Paleozoic age. The magnetite ore of the deposit was densely cut by veinlets of quartz containing abundant gold and poor sulfide. Free high-fineness gold was often encountered in the quartz veinlets, and not infrequently in the magnetite itself as well. Genetically, the gold mineralization of the Kaliostrov deposit is closely connected with the quartz-vein gold mineralization of the Kommunar mine.

In the area situated to the north and west of the Kommunar ore field, namely in the systems of the Izekyul, Maly Cherny Iyus rivers, a number of small bodies of magnetite ores have been noted, such as: Spassky Golets, Nikolsky and Kuznetsovsky springs, Turguyol, Poputnaya Ivanovka, and others. In this same area abundant quartz gold-bearing veins with copper, bismuth, and sometimes scheelite mineralization are developed, and in the past productive gold-bearing placers were worked here. The country rocks of this gold-bearing area are monzonites, monzonite-porphyries, and diorites of small intrusions of pre-Devonian, more likely Caledonian, age.

In the northern part of the Kuznetsk Alatau, within the Mariinskaya

of the gold-bearing taiga, in 1933, in the upper reaches of the Kashkadak River (a tributary of the Kiya River), near the settlement of “Natalyevka,” A. Ya. Bulynnikov discovered pebbles of magnetite ore containing coarse gold in a placer being worked by prospectors. Geophysical work by V. V. Borodin (1933) established here a small deposit of skarn magnetite ores. Prospecting in the 1930s did not yield positive results. Later, in the 1950s, B. D. Vasilyev discovered the Natalyevka skarn gold-ore deposit adjacent to Kashkadak. The skarn ores of this deposit, together with garnet, diopside, and tremolite, contained accumulations of magnetite and sulfides; among the latter we note bismuth minerals, frequent associates of gold.

West of the Natalyevka deposit lies the relatively large Ampalyk skarn deposit of magnetite ores, in which E. A. Babina established the presence of gold [1].

In the southern part of the Kuznetsk Alatau, in the so-called Gornaya Shoria, a considerable number of magnetite skarn deposits are known in the Kondoma River system. Here sulfides are developed in noticeable quantities in the magnetite ore, and the presence of gold has also been noted. During my investigations in 1942, gold was identified in magnetites from pebbles of the Sukharinka River. It should be noted that many magnetite ores of Gornaya Shoria are relatively rich in sulfides, and many gold-bearing placers contain rounded pebbles of magnetite ore, sometimes with gold.

In the same Gornaya Shoria, specifically in the Lebed River system, there is a significant number of placer deposits productive for gold mining. Some 10–12 years ago, during iron prospecting in the Lebed River system, gold was discovered in magnetite-skarn ores. The Maiskoye deposit and its surroundings are currently being studied by N. F. Stolbova. The deposit is confined to the apical part of a large massif composed of granodiorites, syenites, and diorites. The ores of the deposit are represented by garnet-pyroxene skarns with a substantial content of magnetite, often grading into magnetite ores. The author distinguishes two epochs of ore formation. Gold is substantially associated with hydrothermal activity of the post-skarn stage, with a noticeable manifestation of bismuth and bismuth-telluride mineralization. In addition to tetradymite, telluric gold sometimes occurs in the ores. Such ores are rich in gold.

In the Salair Ridge, in the gold-bearing placers of the Kasma and Chebura rivers, gold intergrown with magnetite is often encountered (communication from geologist A. K. Bogdanov). Local geologists regard such gold as an intergrowth of gold with accessory magnetite of diorites, which in the vicinity of the placers form bodies of small intrusions. However, the possibility is not excluded that small magnetite deposits associated with contact-metasomatic rocks of diorite intrusions occur there.

It may also be noted that in the Kuznetsk Alatau (Khakassia), and then in the Gorny Altai and in the Sayans, many gold-bearing placers tend toward areas of magnetite mineralization, especially where bismuth ore mineralization is manifested.

Turning to the foreign literature, we note the deposits of the state of Colorado, USA, in the Ouray district [4]. Here gold-bearing magnetite bodies occur as deposits in skarns and epidotized limestones of the contact zones of monzonite porphyries. The ore is magnetite containing pyrite, chalcopyrite, garnet, epidote, and quartz. The ore of the deposit was characterized by uniform and fairly high-

gold content. Let us also note the skarn-magnetite (with gold) Cable deposit in the state of Montana.

I shall particularly note the very interesting data reported at the First and Second conferences on gold in Tomsk in papers by the geologist Yu. V. Onishchuk. He carried out investigations in Transbaikalia in the area of the Dmitrievskoe quartz-tourmaline gold-bearing deposit, as a result of which vein-type magnetite gold-bearing bodies were discovered. Prospecting in 1966–1968 established the value of this mineralization from the standpoint of gold ore. The gold-bearing magnetite ores contain appreciable quantities of bismuth minerals: bismuthinite, tetradymite, and gold tellurides. Such is the survey material on the gold content of magnetite, more often with skarns, metasomatic mineralization. Let us recall that, according to Goldschmidt, gold is essentially a siderophile element; gold shows a tendency to be associated with iron ores of various genesis.

Exploration geologists and prospectors must take into account this not infrequent association of gold with ores of magnetite skarn (?) and, perhaps, another type of mineralization, which is often accompanied by sulfides, especially with appreciable development of bismuth and tellurium, possibly selenium, ores.

REFERENCES

1. Babina E. A. Petrographic-mineralogical features of the Ampalyk iron-ore deposit. Abstract of Candidate’s dissertation. Tomsk, 1967.

2. Bogdanovich K. I. Ore deposits. Vol. 1, 1913.

3. Bulynnikov A. Ya. The Saktychul gold-ore area and the Kaliostrovskoe gold-bearing iron-ore deposit. Materials on the geology of Western Siberia, 1933, issue 1.

4. Knopf L. Pyrometasomatic deposits. Geology of ore deposits of the Western states of the USA, 1937.