Geochemistry and ore-bearingness of alkaline breeds of Priazovie from point of informative analysis

Volkova T.P., Vyborov S.G.

National technical university, Donetsk, Ukraine

voltep@rambler.ru

 

The basis of the ore-grade mineralization process of any ore element is the law of universal zonality. It will be realized  in transition of ore matter from the dissipated state to concentrated as a result of multi-stage process of differentiation. The alkaline rock are poligenic formations. They are also the result of magmatic or crystallized differentiation. Normal differentiation trend is directed to the increase of silicic acid and alkalinity of the rock. Increase of concentration of lithophilic elements with diminishing of contents of siderophile elements is a general geochemical tendency in transition from early stage of differentiation to late one. Rare elements are included in the group of «remaining» components of magmatic fusion. Therefore many alkaline rock massives initially are geochemical specialized on rare elements. At the evolutional increase of alkalinity of the late differentiate rock there is a considerable increase of concentration of rare elements. The conditional concentrations of rare elements are characteristic for the alkaline rock mass of the crystalline shields. Therefore recurrence and duration of differentiate processes on the prospecting areas  is the main prognosis criterion of rare-metallic deposits. It is setted in Priazovie by an informative analysis.

Theoretical basis of informative analysis is the synergetics. It is set that the processes of differentiation are fixed growth of statistical (dispersion) and informative indexes (informative entropy). The alkalinity of the rock is the parameter of order for the accumulation of rare elements. The evolutionary processes in natural systems are characterized by the growth of information entropy for each subsequent differentiation rock of evolutional row. An informative analysis is directed on  the estimation of the productivity of searching areas on the change of amount information in geological object. Such estimation can be executed on different geological indexes. The increase of information by ore contents characterizes progressive accumulation of ore elements in deposits.

Priazovie is the eastern marginal block of the Ukrainian shield. It is carved out from adjacent Mediumpridneprovsky block by Orechovo-Pavlograd sutural zone. In its constitution are defined west and east microblocks II order, disjointed by the Centralpriazovsky interblock zone. The magmatic zonality of Priazovie is shown in changing from a south-west to the northeast of composition of rocks. The ultrabasic rocks of Korsakskiy synclinorium are replaced the normal and acid rocks of Saltychanskiy anticlinorium, and gradually pass to the subalkaline and alkaline rocks  of East Priazovie. Greater part of alkaline rock of Priazovie is presented  a few intrusive phases. Substantial distinctions are set in distributing of rock-making elements and ore elements in early and late intrusive phases of these structures. The ore-bearing formations characterize containing great amount of light constituents, enrichment alkalines. They are promoting concentration rare metals. Priazovie has a rank of a rare-metallic subprovince. There are the Azov zirconium - rareearth deposit in alkaline sienites of Volodarsky pluton, Mazurovsky and Kalinino-Shevchenkovsky zirconium-tantalum-niobium deposits of the October massif, Petrovo-Gnutovsky fluorite-rareearth deposit and large number show of ore in East Priazovie. They are connected with mezoproterozoic intrusive complexes different composition.

An informative analysis was produced in two stages. On the first stage the blocks of different metallogenic specialization were selected on high-quality indexes (magmatic rocks, fracture tectonics, relief of surface, izoline of the magnetic field) and on the dates of semiquantitative spectrology analyses on 28 ore elements within the limits of all Priazovie In the second phase were analyzed prospective areas according to semi-quantitative spectral analysis of samples of exploratory wells within the October and Volodarsky arrays. The resource estimate is made on the horizontal and vertical sections of the Azovsky and Mazurovsky deposits by chemical analysis of elements of the ore complex. The quantitative estimation of resources is executed within the limits rare-metallic deposits by the index of addition-loss  (positive and negativ values of index of relative  informative entropy). He is got on the basis of cross-correlation analysis  of elements of addition group and loss group. Estimation of addition-loss index conducted in relative units. For comparison  of resources of ore-bearing objects it is necessary to ration the addition-loss index on the number of the examined elements in the system. He allows within the limits of one ore structure to estimate the resources of separate objects. The regular graphic computer model of distributing of indexes was got as the smoothed out value from the unregular  network of basic data. On the first  stage a size of smoothing radius was 5000 meters, and on the second  are from 1000 to 200 meters.

Two ore districts of Priazovie with different metallogenical specialization  are selected on results the first stage of informative analysis. A Western district has sidero-chalkofile geochemical specialization, and  East district – lithophile geochemical specialization. The most high values of informative entropy are set in the subalkaline and alkaline rocks of East Priazovie. All known ore fields are selected the enhanceable (40-50%) values of informative entropy. The further selection of perspective ore structures is executed on the anomalies fields of total entropy of  rare elements contents of within the limits of Volodarskiy  and October massives.

The formation of Volodarsky array occurred in Mesoproterozoic (1800 ± 20 million years) during long magmatic differentiation. As a result the rocks of various composition were formed: from basic to subalkaline. The first phase Volodarsky array represented the stratiform gabbro-syenite intrusion. It takes about 60% of its area in the south-eastern part. The second phase of the array before the intrusion of alkali- feldspathic- hastingsite syenites. Accessory association presented zircon, orthite and pyrochlore. The average content of zirconium is 300 g / t. The third phase of the array before the intrusion of pink of alkali- feldspathic- hastingsite granosyenites and volodarsky granites. The average content of zirconium in them is about 370 g / t. The Azovskiy circular structure is located in the northern part of the Volodarsky array at the intersection of faults sublatitudinal and submeridional direction. In the center of this structure is the syenite pegmatites stock. It represents the fourth and last phase of Volodarsky intrusion. In exocontact of this stock located Azovsky zirconium-rare-earth deposits. The maximal levels of total entropy select the Azovskiy circular structure.

Within the limits of the Azovskiy structure 230 mining holes are bored. South-east part of structure is in detail studied by 84 mining holes.  The detailed  informative analysis of the Azovsky structure (smoothing radius was 500 m²) exposed not only the known Azovskiy rare-earth deposit but also a few new perspective areas. The Azovskiy rare-earth deposit is here  located. Morfometry of the field of this index reflects structural position  of ore bodies. The izoline of the level 400 r.m. of the summary index with practically coincides with the contour of ore body. The part of ore elements (Zr, Ce, La, Y, Yb) in the summary entropy index (28 ore element) makes about 50%. In ore intervals this percent is increased to 96%, in barren intervals falls to 1%.

October array located in the north-western part of the Eastern Priazov’e in the quartz syenites field rasprosraneniya, monzonites and granites of khlebodarovsky stratigraf complex. It was assigned to the most ancient platform formations of nepheline- alkali- syenitic magmatism in the Ukrainian Shield. The area of the array is about 40 km2. It is characterized by a complex multiphase structure and the extensive development of post-magmatic alkaline formations. He referred to the intrusions of the central type. Formation of the intrusion was multistage and very long (over billion years). Definitely magmatic genesis is set for gabbroids of October array. Basic and ultrabasic rocks are best preserved in the north of the October array. In the south and south-east they are found in the form of individual small blocks. Alkaline rocks of the October array are alkaline and nepheline syenites. Nepheline is very unevenly distributed. All alkaline rocks contain unalkaline dark-colored minerals and albite. The appearance of most of the alkaline rocks associated with the stages alkali-sodium- potassium metasomatism. The formation of alkaline rocks associated with the stages of post-magmatic alkaline and carbonate metasomatism (from earlier to later): 1) syenitization; 2) nephelinization, 3) albitization 4) carbonatitizatoin. Productive for rare metals are mariupolites. A characteristic feature of all the type of alkaline rocks is the great variability of structure, texture and composition.

An informative analysis in the October massif rotined all perspective ore manifestation and deposits. The values of the information index in the October array was lower than in Volodarsky. High values of the information rate observed in the center of the array at the intersection of major faults. They were escorted to the field of development mariupolites of Kalinin-Shevchenkovsky and  Mazurovskiy deposits.

The degree of exploration of Mazurovskiy deposit is made by 200 meters between profiles and 50-200 meters between prospecting holes of the profile. The interval of sampling made 1-10 meters. The ore bodies are by floors subhorizontal bedding and clear geological margin. The high values of the summary  addition-loss index  are especially characteristic for Mazurovskiy deposit. It confirms metasomatism genesis of ore-bearing indirectly. The part of ore elements in the total information entropy is low for most of prospecting wells. At intervals of ore it increases and varies from 27 to 70%. The estimation of resources  is executed in the detailed prospecting block. The high values of informative entropy in an ore area distinguish the ore section from barren one.

The conducted research allowed to develop recommendations for a selection and estimation of perspective areas for rare-metallic deposits. In accordance with the prospecting stages it is recommended to conduct the informative analysis. The successive analysis of the anomalous fields of informative entropy allows to select the most perspective areas on every stage. Basic principles and types of estimations are saved. Searching works are characterized low degree of exploration and insignificant contrasty of the field of informative entropy. Most contrastingly perspective areas are selected in the field of summary informative entropy index of contents of typomorphic elements complex. He simply selects ore-controlling structures on every stage of works. The levels of the field of informative entropy change from 20-25% (searching works) to 70% and more (estimation of ore manifestation and deposits). It is depending on sizes and complication  of structure of the studied area. The levels of informative entropy ≥50% testify to appearance potentially of ore-bearing areas. The contrastness and rates of increase of summary informative entropy depends on intensity, duration and amount of the activation stages of the ore-forming system. So the more of them happened in the natural system, so the more contrastingly it is reflected in the field of informative entropy. This method can be used for prognostication of ore-forming structures of any grade mineralization on the any areas of searching works.

 

References:

Volkova T.P. The role of differentiate processes in forming of minerals deposits. // Lectures of Academy of sciences of Ukraine, 2003, №4, p.107-110 (in Russian).

Volkova T.P. Theory and practice of prospecting and estimation of the rare-metallic deposits. – Donetsk: RVA, National technical university, 2003, 102 p. (in Russian).