Geological – Structural and Matallogenic features of the Shuteen Ring Structure

Geological – Structural and Matallogenic features of the Shuteen Ring Structure

B Delgertsogth
Institute of Geology and Mineral Resources, Sector of Regional Geology, P.O. BOX 37/58, Ulaanbaatar, Mongolua.

L. Daramsenqe
Institute of Geology and Mineral Resources, Group of Informatics, P.O. BOX 46/49, Ulaanbaatar, Mongolia.

Abstract
The Shuteen magmata ring structure 14 x 15 square km in size is situated in the Manglain fault systems of the Southern Mongolian Variscan fold belts. This structure is represented by a small subscrustal magmatic activity of late Carboniferous – Early Permain time. Volcanic rocks are composed mainly of andesite-dacite lava flows and their pyroclastic rocks. Within the above mentioned volcanic rocks numerous traces of the ancient volcanic activity are preserved. These include the caldron,. Vent, pipe and subvolcanical bodies. A buried igneous intrusion is located in southern eastern part of this structure and is dominated subalkalic biotite-plagioclase granite and granodiorite T. Sporadic occurrences of diorite and monzonite exist on the periphery.

Mostly terrigenous classic sediments of the Early Carboniferous age are developed in the N-NW part of the Shuteen ring structure and serve as its basement. The Shuteen ring structure is characterized by normal faults of circular and radial shapes. The relatively young fault system that trend NE played an important role in the development of this structure which is subdivided it into two tectonic blocks. The NW part of the structure downthrown while the other block is uplifted

System, which is distributed in the outer part of the Shuteen ring structure there are extensive hydrothermal alterations of various types. The zones are associated with volcanic and plutonic rocks and contain auntie and porphyry copper mineralization. Application of remote sensing techniques gives us possibilities for obtaining new information about this structure.

Introduction
The Shuteen ring structure is about 525 km South of Ulaanbaatar city in the Umne-Gobi almag. The area of this structure is covered by medium – and – large-scale geological survey completed after 1971. The important geological survey at a scale of 1:200000 was conducted by V.I. Goldenberg and specialize metallogenic investigations were done by D.Garamzhay and others. In addition to the above-mentioned studies a large-scale survey and exploration was done during 1981-1983 on this structure. This study serves as the main source for this paper.

Geological position and its inner structure
In terms of regional and structrual geology of htis structure is situated in the Manlain fault system of the Gobi structural-and-for mention zone of the Southern Mongolian Variscan fold belts. The Shuteen ring structure is about 210 km2 in size and is represented small volcano-plutonic structures associated with the subcrustal magmata activity of Late Carboniferous-Early Permian time and is genetically connected with E-W Carboniferous – Early Permian time and is qunetically connected with E-W continental rift zones. Relatively young fault systems that strike NW-SE traverse the continental rift zones and these faults played a decisive role in the initiation of this structure. (Fig. 1) The Shuteen ring structure is composed mainly of andesite-dacite lava flows and pyroclastic sequences and of the buried igneous Shuteen instruction.

The latter consists of subalkalic and calcic-alkasline blotite-plagioclase granite and granodirite and sporadically of diorite and monzonite. Terrigenous clastic sediments of Early Carboniferous age are developed in the N-NW part the Shuteen ring structure and serve as its basement. These were formed in the closing stages of development of the Southern Mongolian Varsican eugeosyncline basin. Layers of these sediments usually are dipping towards he central part of the Shuteen ring structure, which suggests considerable subsidence in its central where extensively developed hydrothermal-metasomatic alteration zones are closely associated with alunite and porpyry copper mineralization.

Features of the fault block structure
Within the area of this structure three major faults-blocks are distinguished. These are based on specific features of the geologic tectonic pattern and on erosion levels. ( See tale 1 and Fig. 2 ) The shuteen ring structure is subdivided into two major tectonic blocks by relatively young fault systems that strike NE-SW. The south-east sector of this fault-block is subdivided into two smaller blocks by faults that strike NW-SE. the paper correlates four areas. (Chan Boqd. Char Tology, Dash Sum and Bayan Chushuu ) See table 2. )

The Char Tology, Dash, Sum, Bayan Chushuu and Dash Sum blocks are also correlated sot that we can use these three blocks for understanding this ring structure. The analysis of 8 elements within the four areas is also correlated (Cu, Mo,Ni,Co,Pb,Zn,Aq, As; see table 3). This geochemical analysis suggests independent copper mineralization. However, the Chan Boqd area has strong correlations of Mo and Zn, Ag and As suggesting some dominant mineralization. The Char Tolgoy area is dominated by a strong Mo and Zn correlation; but the Bayan Chushuu area shows strong Ag, As, Zn, and Mo

Table 2. Geologic Matallogenic characteristics of Shuteen ring structure.

Here all numbers are relative evaluations.

The correlation Analysis result between the block area.

Table 3. The Correlation Analysis results of Geochemistry of the Shuteen ring structure. Elemental contents (%) for Chan Bogd. Char Tolgoy, Dash Sun and Bayan Chushuu

Fig. 1 Geologic and structural sketch of the Shuteen ring structure compiled by using space images and field work.
The downfaulted bocks.
These fault – blocks are downfaulted and cover almost all of the NW part of the structure except that the NE area; Char Tolgoy belongs to the uplifted block. Within the framework of this down faulted block andedesite-dacite volcanic formations and their pyroclastics predominate. Among these volcanic rocks are widely distributed hydrothermal alternation zones which are represented by secondary quartzites, argilizites and prophylaxes.

These hydrothermalites have been formed during postvolcanic activity especially in the solfataric-fumarole processing of Late Carboniferous-Early Permian time. In the secondary quartzites, developing in the Shuteen-Chan Bogd mountain area high – aluminium alunite mineralization was identified.

This gives a forecast for the evaluation of the alunite potential of this area. The majority of these hydrothermal alteration zones were formed before the magmatic intrusion of the Shuteen massifs and before the formation of the porphyry copper ore mineralization. The vertical zonalituy of some ore minerals and elements is defined in the rocks penetrated by boreholes. This tonality indicates a possibility of low temperature, near surface volcanogenic mineralization such as arsenic, lead, gold, silver and complex ores; or of high –temperature ( high-grade) porphyry copper mineralization at certain depth intervals.

Within the previously mentioned hydrothermal alteration zones are restricted electrical anomalies ( using the methods of Caused polarization – CP) with intensivities of 4-6%, sometimes up to 8% which are related to widely impregnated pyritization zones in the rocks.

The uplifted fault – block
The SE part of the Shuteen ring structure consists of different kinds of intrusive rocks as well as numerous minor subvolcanic bodies. The NE part ( the II block) of this fault block is more uplifted than the above mentioned downfaulted block also has a transitional character the geologic-tectonic position between most downfaulted and most uplifted fault-blocks.

In the SW part ( the III block ) of this fault-block the most uplifted block occurs. It includes subvolcanic minor intrusions of grandiosity – porphyry, granite-porphyry and a minor intrusions of grandiosity- porphyry and a number diverse dykes. Both fault-blocks contain porphyry copier mineralization but they have some differences in geologic and structural position. For example, within fault-block-II the most intensive porphyry copper mineralization is associated mostly with minor intrusions of diorite with grandiosity, biotitic granite-porphyry and porphyry copper mineralization is noted in quartz – tourmaline explosive breccia bodies dominantly confined to the exodontists zone between volcanic and the Shuteen granite massifs. The ore bearing alteration processes that occurred during the early stages of mineralization include K- silicate alteration. This gives a Mineral lage dominated by K-feldspar, with biotitic and quartz. During the late stages of mineralization these rocks underwent sericitic alteration producing an assemblage dominated by sericite, with clorite and quartz. Finally, during secondary enrichment the argillic alteration assemblage of kaolinite was accompanied by sericite, chlorite and quartz.

These alteration zones are most closely related to the mineralization, malachite, azurite and rarely covelite and molybdenite.

Fig.2. Fault-block pattern of the Shuteen ring structure.
within fault-block-III granites are developed in the deeper part of the Shuteen massif. Here also diverse prophyritic dykes and minor intrusions are widely distributed. Wall rock alterationa and ore mineralization is similar to fault-block-II.

Geodynamic Condition of Formation. Consider that the volcanic pipe

DL/dR=-K
Where k is coefficient by which
We can use remote sensing data for volcanic characteristics. Therefore we can evaluate pipe depth L, for many volcanic craters. In our case R=10m and 50m, L=1.5 km and 1 km. By the simulation method we find k=10.0

Conclusion
The above mentioned specific geologic and structural features of the Shuteen ring structure are based on the results or large-scale geologic mapping and ore-exploration work carried out directly within the area of this structure, in addition the application of aerial and space images, permits additional new information to be obtained about this structure.

Remote sensing data have been applied in all of these geological studies and serve as major part of these tectonic and structural investigations.

References

M.Korim, B. Delgertsogt., M. Chovan., and I. Fiesh., 1984 The Geologic –structural features and are potential of the Shuteen covano-plutonic magmatic activity. The Geology and Economic Minerals of Mongolia. opp. 159-164 ( in Russian ) Monograph
B. Delgertsogt., 1989. Some specific features of the Shuteen ring structure. Thesis of papers on theme: linear and ring structures of the Mongolian territory. pp. 55-56 ( in Russian)
Delgertsogt., M. Chovan., J. Gregus., 1983 The Geology and Econoc minerals of the Southern Mongolian copper bearing belt. The scientific – production report of the International Geol. Expedition in Mongolia. V-11. pp 20-110 ( in Russian )
M. Chovan., B.. Delgertsogt., J. Gregus., M. Korim, 1985 Metallogenic features of the Southern Mongolian porphyry-copper ore belt. Journal Geologically Pruzkum. V-11. pp. 320-324. ( in Ozechoslovakian language with English abstract )