ON THE PRINCIPLES OF IDENTIFYING ORE FORMATIONS

V. I. BAZHENOV

(Presented to the scientific seminar of the Department of Geology and Prospecting of MPI)

The concept of ore formations was introduced into the literature more than 100 years ago by A. Breithaupt, who understood by this term a small paragenetic group of minerals usually occurring in veins.

Subsequently this term was widely used in the literature by various authors, and its content underwent noticeable changes. This ultimately led to different authors investing different meanings in the concept of “ore formation.” For this reason, some of them [13] proposed abandoning this term altogether. At present, three main trends have taken shape in the understanding of ore formations and, consequently, three principles for identifying them: 1—geochemical, 2—mineralogical, and 3—metallogenic.

1. The geochemical principle for identifying ore formations is the oldest; it was the only one until the mid-1930s. At present it underlies the classifications of ore deposits proposed by G. Schneiderhöhn [16] and F. N. Shakhov [15]. The principal criterion is the assemblage of metals that create concentrations in ore bodies.

The main shortcoming of this principle for subdividing ore deposits is the clearly insufficient detail of the subdivision of deposits. This leads to deposits formed under different geological conditions often being combined into one and the same formation. Thus, for example, using the geochemical principle, quartz–wolframite, quartz–hübnerite, quartz–ferberite, and quartz–scheelite veins are combined into a single tungsten formation of vein deposits. All these types of tungsten-bearing veins differ from one another in many geological features: in the temperature and depth of formation, in the relationship of mineralization to magmatic rocks, in the paragenetic relationships of tungsten with other metals, in the character of wall-rock alterations of the host rocks, in the time of appearance of the deposits at different stages of development of the Earth’s crust, etc.

1. The mineralogical principle for identifying ore formations appeared in the mid-1930s after the publication of the well-known works of Academician S. S. Smirnov. From that time it became fairly widespread and was made the basis of a whole series of classifications of ore deposits [1, 2, 10, 11]. In this approach, to identify ore formations, authors use either characteristic minerals or stable paragenetic mineral associations.

The application of the mineralogical principle in its pure form suffers from a number of shortcomings. First, on the basis of the principle under consideration some authors distinguish a large number of ore formations. Thus, V. M. Petrov [12], among the molybdenum deposits of Uzbekistan alone, distinguishes 10 ore formations, although this certainly does not exhaust all the types of molybdenum deposits known in nature. For the tungsten deposits of Uzbekistan, M. S. Kuchukova et al. [9] distinguish 11 ore formations. The number of examples in which a large number of ore formations are distinguished according to mineralogical criteria could be considerably increased. The abundance of ore formations makes the use of such classifications difficult and ultimately leads to the fact that minor details of differences in the mineralogical composition of ores obscure and mask those features which truly unite these deposits.

Second, the scope of the ore formations being distinguished often proves to be very unequal. Thus, for example, I. G. Magakyan [11] assigns to the formation of ore-bearing skarns the entire genetic type of contact-metasomatic deposits of iron, cobalt, copper, tungsten, molybdenum, and other metals. At the same time, among postmagmatic tin deposits alone, tin–tungsten–molybdenum greisens, quartz–cassiterite, and cassiterite–sulfide formations are distinguished.

Third, ore deposits, especially those of hydrothermal genesis, are characterized by an uneven distribution of mineral matter. On the one hand, this may be connected with manifestations of horizontal or vertical zoning of mineralization, and on the other, with the local manifestation of mineral associations of one or another stage of mineralization. Therefore, as F. N. Shakhov [15] noted, within a single ore field, according to mineralogical criteria, ore bodies may be distinguished that belong to different ore formations.

Fourth, the use of the mineralogical criterion for distinguishing ore formations leads, in some classifications of ore deposits, to the inclusion within one and the same formation of clearly heterogeneous deposits belonging to different genetic types. For example, on the basis of similarity in the mineralogical composition of the ores, such heterogeneous deposits are sometimes united into a single group as lead–zinc skarn deposits (of the Tetyukhe type), quartz veins with sphalerite and galena (of the Sadon type), and also complex metasomatic deposits of lead–zinc ores (the deposits of the Karatau Range).

Finally, it should be noted that the absence of reliable objective criteria for distinguishing ore formations makes this process to a considerable extent subjective.

1. The metallogenic principle has recently been developed in the works of V. A. Kuznetsov, R. M. Konstantinov, I. N. Tomson, V. S. Domarev, D. I. Gorzhevsky, and others [4, 5, 6, 7, 8, 14]. The distinction of ore formations according to this principle is carried out with consideration not only of characteristic mineralogical (or geochemical) associations, but also of the geological position of ore deposits within the general structure of the region. E. E. Zakharov [6] proposes, in this connection, taking into account the following properties of deposits: features of the material composition of the ores, features of the enclosing rocks and their alteration, geological conditions of occurrence of the deposits and regularities in the distribution of mineralization, the morphology of ore bodies, the position of ore deposits in regional structures and metallogenic provinces, the scale of mineralization, and so forth.

Of interest is the distinction of a number of ore formations carried out by I. N. Tomson and R. M. Konstantinov [14]. In this, it is estab—

gradual transitions of some ore formations into others are observed, depending on the intensity of manifestation of particular stages of mineralization.

V. S. Domarev [4] invests a somewhat different meaning in the concept of an ore formation. He believes that the identification of ore formations by a metallogenic or mineralogical criterion suffers from uncertainty because ideas about the principal industrial components of ores are not constant and change over time. Therefore V. S. Domarev proposes to distinguish ore formations by the sum of geological features, understanding them as “groups of deposits similar in their geological characteristics and possessing a complex of geological features inherent only in this group.” Thus, the author distinguishes a chromite formation, a pyrite formation, cupriferous sandstones, etc.

1. The views of L. A. Bykov [3] stand apart; he understands by an ore formation the entire aggregate of ores and near-ore altered rocks of a region that have one and the same age, or one and the same upper age boundary in the form of a regional unconformity surface. It is difficult to agree with such an understanding of ore formations, since in this case one and the same group may unite ore deposits that differ not only in material composition but also in genetic type and, often, in age. Under such a principle, the specific features of the connection between mineralization and particular types of geological formations may also be lost. Another shortcoming is the circumstance that, in a number of regions, especially in areas of development of Lower Paleozoic and Precambrian folding, the upper age limit is not always established sufficiently clearly and unambiguously.

From consideration of the main principles for distinguishing ore formations, it may be concluded that the metallogenic principle appears to be the most rational. The identification of ore formations must be based on a comprehensive study of ore deposits. In doing so, alongside the features of material composition, geological factors must also be taken into account, among which the main ones are the following: magmatic complexes with which the mineralization is associated, the position of deposits in large regional structures, the character of near-ore alterations of the enclosing rocks, the temperature of formation of the principal productive mineral associations, etc. In any region there may occur ore deposits having a similar material composition but associated with magmatic complexes of different ages. Obviously, for purposes of metallogenic analysis it is expedient to assign them to different ore formations. Thus, ore formations should include deposits that possess similar geological conditions of formation.

The use of the term “ore formation” should by no means be set in opposition to the concept of “genetic type,” as is done by some authors who propose, alongside genetic classification, to create one on a formational basis. It seems to us that the two classifications by no means exclude one another, but mutually complement one another. At the same time, an ore formation is a smaller classification unit than a genetic type. Therefore the introduction of the concept of “ore formation” into genetic classification is a new step in the development of the genetic classification of ore deposits. It makes it possible to distinguish, among deposits of the same type, smaller groups that differ from other analogous groups in their material composition and genetic features. Investing such content in the term under consideration, it may be considered that, within the limits of a single genetic type, for each of the metals there may be distinguished several ...

several ore formations. Therefore, the number of ore formations within a single genetic type may be quite large, although in metallogenic analysis of individual regions, where the diversity of ore deposits is relatively small, the formations are unlikely to be numerous.

Taking into account the considerations set forth above, an ore formation may be defined as a group of deposits distinguished by the similarity of stable mineral associations formed under similar geological conditions and connected with one another by a unity of genesis.

The nomenclature of ore formations is currently established in different ways. Often the principal minerals included in the ores have been used as the criterion. As a result, ore formations identical in mineralogical composition appear in different genetic types, or, as noted above, deposits belonging to different genetic types but having a similar composition of the main productive mineral associations have been combined into one and the same formation. It seems advisable, in the name of an ore formation, along with the features of the composition of productive mineral associations, also to reflect the geological features of their formation and their affiliation with one or another genetic type. Thus, for example, one may speak of skarn scheelite, magmatic titanomagnetite, medium-temperature gold–quartz vein formations, etc.

Apparently, it is not expedient to create a special classification of ore deposits on a formational basis that duplicates the genetic classification. Ore formations should be included as a component part of a unified classification of ore deposits constructed according to the genetic principle. At the same time, two additional systematic units may also be introduced into such a classification: the family of ore formations and the mineral type.

A family of ore formations represents a larger unit in the systematics of ore deposits. By this term we understand a group of ore formations combining ore formations of one and the same metal and belonging to one and the same genetic type. In other words, the concept of a family of ore formations corresponds in content to an ore formation distinguished according to a geochemical or metallic principle. Thus, for example, the hydrothermal vein quartz–wolframite, quartz–hübnerite, quartz–scheelite, and quartz–ferberite ore formations may be combined into a family of tungsten ore formations.

Within the class of vein deposits, families of ore formations may be distinguished: 1) tin, 2) tungsten, 3) bismuth and molybdenum, 4) copper, 5) gold, 6) iron, 7) lead and zinc, 8) silver, 9) mercury, 10) antimony, 11) a five-element family, i.e., of those metals which, in this genetic type of deposits, create industrial concentrations.

The mineral type is undoubtedly a smaller unit in the classification of ore deposits. The introduction and use of this unit makes it possible to identify minor variations in mineralogical composition within deposits of one and the same ore formation, caused by facies reasons and other local factors. By this term we understand a group of ore deposits belonging to one ore formation, formed from solutions of identical composition and possessing a similarity in the mineralogical composition of the ores. Differences in mineral types, and consequently in their identification, may in some cases be caused by a locally uneven manifestation of individual stages of mineralization. The nomenclature of mine—

...of real types should be constructed according to the most characteristic minerals included in the productive mineral associations. Thus, for example, among the medium-temperature gold-quartz vein deposits of the Kuznetsk Alatau, the following mineral types may be distinguished: 1) gold-bismuthine (tellurobismuthine), 2) gold-arsenopyrite, 3) gold-polymetallic. All these deposits are associated with intrusive rocks of one and the same magmatic complex; they are characterized by similar hydrothermal wall-rock alterations. The observed differences in mineralogical composition are explained by local causes, while between the gold-arsenopyrite and gold-polymetallic mineral types gradual transitions are established, depending on the intensity of manifestation of the quartz-pyrite-arsenopyrite and quartz-polymetallic stages of mineralization.

Thus, the family of ore formations, the ore formation, and the mineral type constitute the smallest subdivisions of a unified genetic classification of ore deposits. If a parallel is drawn with biological classification, these units may correspond to the concepts of “family,” “genus,” and “species.”

It may be hoped that the use of these concepts in geological practice will make it possible to divide deposits into smaller groups in order to study the questions of their genesis in greater detail, to establish the regularities of their distribution in the earth’s crust and within metallogenic provinces and structural-facies zones. This, in turn, will undoubtedly contribute to increasing the effectiveness of geological investigations.

LITERATURE

1. A. G. Betekhtin. On mineragraphy. Izv. AN SSSR. Ser. geol., No. 6, 1945.

2. A. Ya. Bulynnikov. Gold-ore formations and gold-bearing provinces of the Altai-Sayan mountain system. Tomsk, TSU Publishing House, 1948.

3. L. A. Bykov. On the question of ore formations and ore facies. Tr. Sredneaziat. polit. inst., issue 6, 1959.

4. D. I. Gorzhevsky. On the metallogenic significance of ore formations. Geol. rudn. m-nii, No. 6, 1964.

5. V. S. Domarev. Ore formations as historical-geological formations. Geol. rudn. m-nii, No. 4, 1968.

6. E. E. Zakharov. On certain questions of the classification of ore deposits. Sov. geol., No. 9, 1965.

7. R. M. Konstantinov. Methods of study and criteria for distinguishing magmatogenic ore formations in large-scale metallogenic investigations (on the example of Eastern Transbaikalia). In: Endogenous ore formations of Siberia and the Far East. “Nauka,” 1966.

8. V. A. Kuznetsov. Genetic groups and formations of endogenous deposits and their significance for metallogenic analysis. In: Endogenous ore formations of Siberia and the Far East. “Nauka,” 1966.

9. M. S. Kuchukova, M. I. Ismailov, U. Rakhmedov. Endogenous formations of tungsten. In: Endogenous ore formations of Uzbekistan, vol. 1, Tashkent, 1966.

10. I. G. Magakyan. The principal industrial families and types of ores. Zap. Vs. Min. obshch., No. 4, 1950.

11. I. G. Magakyan. An attempt at classification of ore formations of the USSR. Geol. rudn. m-nii, No. 5, 1967.

12. V. M. Petrov. Endogenous formations of molybdenum. In: Endogenous ore formations of Uzbekistan, Tashkent, 1966.

13. P. M. Tatarinov. Conditions of formation of deposits of ore and non-ore mineral resources. Gosgeoltekhizdat, 1963.

14. I. N. Tomson, R. M. Konstantinov. On the relationship between ore formations, using the example of certain districts of the Pacific ore belt. Geol. rudn. m-nii, No. 4, 1961.

15. F. N. Shakhov. The principle of formations in the systematics of deposits created by hot solutions. In: Endogenous ore formations of Siberia and the Far East. “Nauka,” 1966.

16. G. Schneiderhöhn. Ore deposits. IIL, 1958.