ture of the study area, the images obtained during the digital elevation model processing by MGR at values t = 1, 16, 64 were used.

The applied procedures of the digital elevation model processing by MGR are visually increasing a degree of indentation of the topography (Figure 3). In the transformed image, this characteristic is demonstrated by different tones of grey. The less indented segments (blocks) are colored black and dark-grey, the most indented ones are shown in different tones of grey and light-grey. One can consider textures as an independent object, i.e., zones with clearly manifested morphometric indications (sedimentary basins, mountain massifs, built up of different intrusive, sedimentary and effusive rocks, etc.) are discriminated as a result of processing.

The texture peculiarities may serve as an indicator of rock composition and major lithological and petrographic complexes. The character of the boundaries between different types of the topography testifies to the interrelationship between different strata, indicating whether the contact is normal stratigraphic or tectonic one.

Stripe linear anomalies are commonly identified with linear bodies (dikes) of intrusive rocks, stable to weather-

(a) (b) (c)

Figure 3. Basic digital elevation model of the Uchur-Maya basin (A) and examples of its processing (B, C).

ing, with steeply dipping strata of deposits and differently oriented faults. The ring anomalies correspond to small size intrusions, volcano-tectonic depressions and intrusive-dome structures. The elements of the hydrological network allow detecting the most prominent regional geological objects including faults and folded structures.

Further image processing was carried out applying the program technique LESSA (Lineament Extraction and Stripe Statistical Analysis), implemented in the program WinLESSA [3]. The program provides the uniform numerical description of images showing different type schemes and digital elevation models, the detection of linear elements of the pattern and description of their properties in a way common for the geological studies. In the search for the linear elements, the rectified segments of the boundaries of areas differing in brightness have been distinguished in a halftone image. During the computation, the size of elementary linear elements is given with an account of the initial image resolution, the geological features of the study area and the objectives set. The analysis of the data obtained during the computation provides the distribution of locally dominating orientations over the study area, the uniform and anomalous areas in terms of orientation properties, etc.

As a final result, the following maps have been done for the study area: those of lineaments exhibiting different degree of their manifestation, rose-charts of lineament orientation over the study area, boundaries of changing pattern (structure) of rose-charts, extension lines of roses, the distribution density of elementary linear elements, etc. The portion of the data obtained, particularly, the distribution of lineaments and density distribution of elementary linear elements of the topography (Figures 4 and 5), which exhibits a degree of indentation of the topography, has been used in the present study for the structural construction and further interpretation.

3.3. Metallogeny

In the Uchur-Maya basin there have been revealed tantalum, niobium, zirconium, apatite, REE, polymetallic, copper, molybdenum, vanadium, gold and uranium deposits (Figure 2). The deposits and occurrences of gold, vanadium, copper, molybdenum, polymetals and uranium of predominantly stratiform type are localized in the zone of Pre-Calymmian structural-stratigraphic unconformity and in the platform cover [7,23]. In the Neoproterozoic ultrabasic alkali intrusions of the central type, niobium, tantalum with uranium, zirconium and REE deposits have been found. They are clustered in the Arbarastakh, Ingili, Gornoye Ozero, Povorotnyi and Gek massifs [24,25] (Tables 1 and 2; Figures 4 and 5).

Several types of ore-bearing rocks have been discovered including carbonatites, pyroxene-apatite-phlogopitemagnetite-calcite metasomatites and intensely albitized rocks [24]. The complex of minerals includes zircon, fluorite, hatchetolite, руrochlore, baddeleyite, perovskite, betafite, dysanalyte, monazite, zircon, zirconolite, bastnaesite and columbite. The amounts of magnetite (3% - 5%), pyrite (3% - 5%), apatite (2% - 3%) and, also, ilmenite, sphen, hematite and other more rare minerals to 1% content were detected. The niobium content ranges from 0.2% to 0.5% - 1.2% in the ore zones among carbonatites and metasomatites of the first type, the percentage of tantalum is 0.002% - 0.1%, that of uranium reaches 0.003% - 0.3%, thorium amounts to 0.005% - 0.03%, strontium content attains 0.7% - 1% and the amount of phosphorus exceeds 10%.

The ores were disclosed in albitites for the first time. They were found in the western endoand exocontact zones of the Arbarastakh intrusion and exhibit higher

Table 1. Type and location of deposit fields in the UchurMaya area.

uranium (to 0.28%), niobium (to 2.5%) and tantalum (to 0.12%) contents as compared to the ores associated with pyroxene-apatite-phlogopite-magnetite-calcite metasomatites and carbonatites.

In Ediacaran rocks the stratiform deposits of zirconium, polymetals, gold and REE of cerium group were detected. The age of mineralization was not determined. Pb isotopic age determinations yield the Neoproterozoic to Early Paleozoic age range of the ore mineralization.

In the Mesozoic, intense volcanism and intrusive magmatism took place in the Uchur-Maya depression thus forming the Ket-Kap volcano-plutonic gold-bearing zone. This zone is notable for the mixed set of the morphological types of ores (stockworks, stratiform lodes in silicitolites and argillizite-sericite metasomatites).

The formational types of gold mineralization are as follows: gold-sulfide-scarn, vein gold-quartz, gold-quartzhydromicaceous and gold ore in Ediacaran silicitolites (jasperoids). Here, not less than ten predominantly small gold ore deposits have been prospected. High gold pro-

Table 2. Type and location of ore occurrences in the UchurMaya area.

Figure 4. Sketch-map of lineament distribution for the Uchur-Maya basin from processing results using programs “Modulus of gradient of the topography” [1,2], “WinLessa” [3] and locations of major ore deposits and occurrences. Stars show deposits, circles indicate occurrences; numbers before symbols correspond to the numbers given in Tables 1 and 2.

duction capacity of this structure is predetermined by specific conditions of its formation. The majority of gold-ore objects of the Ket-Kap zone are closely associated with massifs of small sub-alkali and alkali intrusive rocks of the Ket-Kap complex, but there are objects where this association is not so obvious. The exploration prospects for the major stratiform “Carlin”-type deposits are associated with silicitolites in the Ediacaran Ust’-Yudoma Suite.

4. Results

For all the diversity of metallic minerals and their widespread distribution in the Uchur-Maya depression area, clearly displayed lithological and structural regularities of their localization are observed.

In order to reveal the relationship of ore occurrences of the Uchur-Maya depression with fault tectonics, there have been compiled and interpreted the map of MGR of the digital elevation model for the study area and those of the distribution of lineaments and density distribution of elementary linear elements (Figures 4 and 5).

All the data obtained were integrated into the ArcGis 9.3 Project, where the linear fault network layer based on manual interpretation of the digital elevation model

Figure 5. Scheme of density distribution of elementary linear elements of the Uchur-Maya basin from processing results using programs “Modulus of gradient of the topography” [1,2], “WinLessa” [3] and locations of major ore deposits and occurrences. Light-colored lines bound the areas with the maximum density of elementary linear elements.

processed by MGR and the layer of known deposits and occurrences of rare, nonferrous and radioactive metals have also been complemented.

The analysis of the map of visual interpretation (Figure 2) has shown distinctions in the eastern and western parts of the depression either in terms of development of differently oriented fault structures or intensity of their manifestation in the area. In the eastern part of the depression, the meridional and submeridional faults are most common. They are dominantly distributed in the Yudoma-Maya trough and, practically, do not overcome its bounds (Figure 4). It has been established a clear association of gold, uranium and polymetallic mineralization with these faults. Besides, they are controlling the bodies of ultrabasic alkali rocks with tantalum-niobium and REE deposits (Gornoye Ozero, Povorotnyi, Gek and Khamninsk). Consequently, one may assume a close relationship of the detected deposits with the meridional and submeridional faults.

In the central and western parts of the depression, the ore objects are localized in the northeastern stripe of 100 - 150 km width and about 400 km extent bordered by the Uchur-Ust’-Yudoma and Khaikan-Kerpyl deep faults. Within the stripe, the ore mineralization is controlled by the submeridional, northeasterly striking, and, more rarely, sublatitudinal tectonic faults.

The dominating role belongs to the northeasterly trending faults with insignificant participation of the submeridional and northwesterly oriented ones. The orecontrolling role of the Khaikan-Kerpyl fault is most clearly displayed. It controls the Konder platinum deposit, the Vasilek and Tomptokan gold deposits, the Adargai anomalous field with complex U, Mo, Ag, Ni, Co, Cu and As mineralization, the Khangas and Ugdan uranium occurrences and the Amulikan River basin gold occurrences in the area extending for 180 km from northeast to southwest. The Algaminskoe uranium-zirconium deposit is controlled by the sublatitudinal fault. A significant part of the objects of this stripe is localized in the gentle shearing areas in the zone of Pre-Riphean structuralstratigraphic unconformity and in scarns in exocontact zones of the Mesozoic granitoid intrusions.

In Figure 4, differently oriented linear lineaments, notably meridional, northeastern and northwestern, are distinctly displayed. The meridional and submeridional faults are mostly widespread, being the most ancient ones due to their control of the formation of meridionally extended Uchur-Maya depression. They are nonuniformly distributed over the depression area. The eastern and western stripes exhibiting the meridional lineament concentration are noticeable. Distinct control of ore deposits and occurrences by the meridional and submeridional lineaments is observed in the Yudoma-Maya trough and the southwestern part of the depression. The proper ore objects are in the majority of cases controlled by junctures of intersection of the meridional lineaments with the northeastern and northwestern ones.

The density distribution map of elementary linear elements of the topography (Figure 5) exhibits the intensity of distribution of differently oriented cracks per unit square. The less disturbed areas are shown in light-grey, whereas the most disturbed ones are colored black. The areas with the maximum density of elementary linear elements are nonuniformly distributed in the UchurMaya depression (Figure 4). A number of such areas are distinguished in the northern part of the Yudoma-Maya trough, in the central part and in the southwest of the depression area. The most clearly manifested relationship of ore occurrences with the maxima of linear element distribution is established for the southern part of the depression (Figure 5). Practically, all presently detected occurrences of gold, uranium and other elements are concentrated within this contoured area. In the central part of the depression, where the most intense area of the linear element distribution is distinguished, the Algaminskoe uranium-zirconium and Ingili uranium—rare metal—REE deposits have been discovered. A sparse set of ore occurrences in this area is explained by extremely poor prospecting of this territory, which we rank promising. As a matter of fact, the same should be noted for the area in the northern part of the Yudoma-Maya trough. This area is worthy of great attention, because polymetallic, gold ore and rare metal deposits have been found to the east and south of it in the trough, in the fields of less intense areas.

5. Conclusions

As a result of the studies carried out, it has been established a clearly displayed control of the ore deposits and occurrences by the faults.

1) In the eastern part of the Uchur-Maya depression and in the Yudoma-Maya riftogenic trough, the ore mineralization is controlled by the extended (hundreds of kilometers) meridional tectonic fault zones;

2) In the central and western parts of the depression area, the ore objects are localized in the northeastern stripe of 100 - 150 km width and of about 400 km extent, bordered by the Uchur-Ust’-Yudoma and Khaikan-Kerpyl deep faults. Within the stripe, the ore mineralization is controlled by the submeridional, northeasterly striking, and, more rarely, sublatitudinal tectonic faults;

3) The maxima of the concentration of ore deposits and occurrences are observed in the segments with high density of the meridional lineaments. The relationship of the deposits with the maximum density of linear elements is revealed in the central and southwestern parts of the depression and is practically not exhibited in the Yudoma-Maya trough.

The Uchur-Maya trough is the prospective structure for exploration of gold, uranium, polymetallic, silver, molybdenum, copper, nickel, platinum, rare and REE deposits of unconventional formational types, having no analogs in the Russian Far East area.

6. Acknowledgements

The authors are thankful to the anonymous reviewers whose remarks and suggestions contributed to better understanding of the manuscript by the readers. Thanks are also due to N. N. Kovriga, E. Yu. Didenko and O. M. Men’shikova for their assistance in the preparation of the manuscript.

The studies have been supported by the Far Eastern Branch of the Russian Academy of Sciences (RAS) (Program of Satellite Monitoring and Project No. 12-I- 0-08-004) and the Russian Foundation for Basic Research of the RAS (Projects Nos. 12-05-00088a and 12- 05-91158).

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