EXPERIENCE IN APPLYING THE RESULTS OF SPECTRAL ANALYSIS TO CLARIFY THE GENETIC RELATIONSHIP OF DIKES WITH AN INTRUSION

D. K. OSIPOV

(Presented by Professor A. M. Kuzmin)

As a result of the work of A. E. Fersman [10], A. N. Zavaritsky [5], Kh. M. Abdullaev [1], and many other Soviet (D. S. Belyankin, 1947; N. I. and M. B. Borodaevsky, 1947) [2, 3, 4, 6, 7] and foreign geologists [11], the geological literature has accumulated and generalized extensive and exceptionally valuable data on the geological position, composition, and structure of dike formations and, in particular, aplites and pegmatites.

At the same time, a whole series of questions in this problem has been covered in the literature extremely inadequately, a point quite rightly emphasized by the researcher Kh. M. Abdullaev [1].

In the present article an attempt is made to clarify the geochemical continuity between aplite dikes and a granodiorite intrusive massif, using as an example one of the districts of Gornaya Shoria, and employing the results of semiquantitative spectral analysis.

Before proceeding to a description of the methods and results of the work, it is necessary briefly to characterize certain features of the geological structure of the area of investigation.

The area studied is located in the contact zone of a granodiorite massif of pre-Devonian age. The enclosing rocks are limestones, amphibolites, and hornblendites. This entire complex of rocks is broken by numerous series of disjunctive disturbances of northwestern and northeastern trends. Both in the enclosing rocks and in the intrusive massif, mining and drilling operations have established the presence of numerous dikes of plagiaplites and aplites.

According to drilling data, the latter in a number of cases proved to be accompanied by hydrothermal ore mineralization. It should be added that the area described is covered by a continuous and comparatively thick mantle of loose deposits.

Naturally, in studying an ore field under such geological conditions, the question of clarifying the genetic relationship of the rocks of the vein complex with the intrusive massif, among which or in the immediate vicinity of which they occur, became especially acute.

Although in all works devoted to this question the geochemical and petrochemical continuity of the composition of dikes from the composition of the indicated intrusions is emphasized—that is, their genetic relationship is noted—some local geologists in the area described genetically linked the aplite dikes and their analogues with younger intrusions of syenito-

of composition, small bodies of which are developed 5 km south of the work area.

In connection with this, in the summer of 1957 the author collected samples of aplites, plagiaplites, and granodiorites in mine workings and from drill cores. In the latter case, samples were taken both near the dikes and at considerable distances from them. From each sample, 3–4 thin sections were prepared for microscopic study. Then, after detailed macroscopic and microscopic study, half of each hand specimen was crushed to 0.5–0.7 mm. After crushing, the material was thoroughly mixed and divided into two parts. From one part, under a binocular microscope, a monomineralic plagioclase charge was selected for spectral analysis; the other part of the sample was submitted in its entirety for spectral analysis.

Fig. 1. Summary circular diagrams of granodiorites (1), aplites (2), and plagiaplites (3) according to the results of semiquantitative spectral analyses.

Fig. 2. Graph of element contents in plagioclases of granodiorites (1), aplites (2), and plagiaplites (3) (Gornaya Shoriya) according to the results of semiquantitative spectral analyses.

The results of the semiquantitative analysis of the rocks were depicted in the form of circular diagrams (Fig. 1), following the method of D. A. Shimer [11], and also in the form of graphs (Fig. 2), where the content in percent was plotted along the abscissa axis, and the elements along the ordinate axis. In this, the scales were chosen in accordance with the content of each element.

The work carried out showed that the aplites and plagiaplites have many mineralogical-geochemical features in common with the rocks of the granodiorite massif. This is confirmed by the factual material presented below.

If we turn to the generalized circular diagrams (Fig. 1), we see a striking qualitative similarity of the circular diagrams of apـ

…aplites and granodiorites. True, in quantitative terms these identities are, in individual cases, somewhat violated, which is quite natural. Such deviations are evidently due to the different physicochemical conditions arising at particular stages in the evolution of a magmatic chamber [9, 1].

The results of processing the spectral data, shown in the graph (Fig. 2), are exceptionally indicative in this respect. Here the geochemical continuity in the composition of the feldspars of granites (1), aplites (2), and plagioaplites (3) is expressed so clearly that it leaves no doubt on this point. For comparison, Fig. 3 gives a graph of the contents of the same elements in the feldspars of the Iedygem granodiorites and granites of the Karasu Altai, constructed by the author from spectral-analysis data borrowed from the candidate dissertation of A. I. Bazhenov (Tomsk Polytechnic Institute). Comparing Fig. 2 and Fig. 3, we see the difference in the geochemical features of each of the indicated massifs of intrusive rocks. This circumstance well confirms the known proposition that there is a close genetic connection between dike rocks and particular intrusions in general, and with specific massifs in particular [1].

In addition, microscopic study of thin sections from the aplites and granodiorites of this area showed the commonality of the mineral composition of these rocks.

Fig. 3. Graph of the contents of elements in the plagioclases of granodiorites (1) and granites (2) (Altai) according to the results of semi-quantitative spectral analyses.

Thus, a detailed study of the mineralogical composition of the dikes of plagioaplites, aplites, and intrusive rocks of the granodiorite massif, as well as elucidation of their geochemical features from spectral-analysis data, gives grounds to assert that there are many common mineralogical-geochemical features among the indicated rocks, which make it possible to judge their genetic connection. At the same time, establishing the genetic kinship of these formations provides a basis for clarifying the genetic connection of mineralization with the intrusion.

The author is aware of the insufficient development of this method, but at the same time is deeply convinced that its further development and application, especially in covered areas, will contribute to a more objective solution of the question of the genetic kinship of magmatic rocks, spatially associated dike formations, and mineralization.

LITERATURE

1. Abdullaev Kh. M. Dikes and Mineralization, Gosgeoltekhizdat, 1957.
2. Belyankin D. S. On the question of the present state and prospects of the doctrine of magmas and magmatic rocks. Izv. AN SSSR, geological series, No. 5, 1947.
3. Borodaevskii N. I. and Borodaevskaya M. B. The Berezovskoe Ore Field. Metallurgizdat, 1957.

1. F. I. Volfson. Problems in the Study of Hydrothermal Deposits, Publishing House of the Academy of Sciences of the USSR, 1953.

2. A. N. Zavaritskii. Granites and Aplites, ZVMO, No. 2, 1950.

3. V. S. Koptev-Dvornikov. Regularity in the Formation of Intrusive Granitoids, Based on the Example of Central Kazakhstan. Proceedings of the Academy of Sciences of the USSR, Geological Series, No. 4, 1952.

4. O. S. Polevoi. Formation of Vein Rocks of Acidic Intrusions. Transactions of the IGN, Academy of Sciences of the USSR, issue 107, 1950.

5. M. G. Rub. The Relationship of Vein Rocks with Mineralization in the Southwestern Part of Primorskii Krai. Soviet Geology, collection 51, 1956.

6. S. D. Turovskii. On a Mineralogical-Geochemical Indicator of the Genetic Connection of Postmagmatic Ore Occurrences with Intrusive Rocks. Proceedings of the Academy of Sciences of the USSR, Geological Series, No. 6, 1953.

7. A. E. Fersman. Pegmatites. Publishing House of the Academy of Sciences of the USSR, 1932.

8. D. A. Shimer. Spectrographic Analyses of Granites and Pegmatites of Novaya Anglia. Rare Elements in Igneous Rocks and Minerals (collection of articles), IL, 1952.