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Geological collaboration between Japan and Mongolia
Terumasa NAKAJIMA(Mineral and Fuel Resources Department, GSJ)
1998
vol. 49 (6) P. 237-238
Phanerozoic felsic magmatism and related mineralization in Mongolia
Ochir GEREL(Mongolian Technical University)
1998
vol. 49 (6) P. 239-248
3 figs.
Keywords: Phanerozoic, felsic magmatism, mineral deposit, rare metal, Mongolia
Abstract: Mongolia situated between the Siberian craton in north and the Northern Chinese and Tarim platforms in south was the arena for multiple orogenies which resulted in the complicated geological structures of Precambrian to Cenozoic systems. Granite magmatism occurs in Early, Middle and Late Paleozoic and Mesozoic Periods. Granites were generated at Phanerozoic convergent plate margins, including island arc, plate margin and continental collision zone. Majority of economically important mineral deposits and occurrences are related to Late Paleozoic and Mesozoic granites, generated in mature continental crust. Porphyry-copper-molybdenum, skarn, pegmatite, rare metal, rare earth, and Pb-Zn-Ag mineralization are associated with such granites. This paper will list some representative deposits of granitic affinity in Mongolia.
K-Ar dating of granitoids and hydrothermal micas from the northern part of Kherlen Depression, Mongolia
Satoshi Murao(Mineral and Fuel Resources Department, GSJ), Danjindorjiin Dorjgotov(MONRUD Co., Ltd.) and Tsagaanbilegiin Tseden(MONGOLYN ALT Corporation)
1998
vol. 49 (6) P. 249-255
6figs., 1 table
Keywords: Mongolia, Kherlen Depression, Mongon-Ondor deposit, Ondor tsagaan deposit, Tsagaan chuluut deposit, Tsenker gol Complex, Bor-Ondor Complex radiometric age, monoascendent zoning, polymetallic ore
Abstract: We have determined the K-Ar ages for micas of granitoids and hydrothermal deposits in the Kherlen Depression, one of the prospective regions of eastern Mongolia. According to geologic evidences, the granitoids belong to Triassic, Jurassic or Carboniferous in age, and are accompanied by many hydrothermal deposits. Some large stocks are considered to have developed during the Carboniferous or Triassic Period, while small plugs show evidences of Jurassic-time intrusion. Among the hydrothermal deposits in the depression, the Ondor tsaggan (Mo-W-Be) and Mongon-Ondor polymetallic (Zn-Sn-Pb-Ag) deposits within the Ondor tsagaan ore field were selected for the age determination. The result showed that a granitic plug near the Ondor tsaggan ore field has 191 Ma, while hydrothermal micas from Ondor tsagaan deposit and Mongon-Ondor deposit show the age of 174 and 175 Ma respectively. In addition to these, two ages for igneous mica from a Carboniferous complex were obtained to be 273 and 308 Ma.
Mineral deposits in the depression are distributed along the boundary between Devonian sedimentary rocks and Carboniferous granitoids, which implies that mineralization mainly took place during the Carboniferous Period being related to large-size stocks. But our geochronology indicates that several mineralization episodes were existed in the Kherlen Depression and especially Jurassic magmatism was important for polymetallic mineralization.
Also it is noteworthy that the Mo-W-Be and Zn-Sn-Pb-Ag zones (deposits) of the Ondor tsagaan ore field have mostly the same age, 174 and 175 Ma. This fact indicates that two zones in this ore field are probably a product of single pulse solution from a felsic magma. In addition geologic setting indicates that a polymetallic ore field, 10-20 km2 in dimension, could be formed around the apex of such small plug. In eastern Mongolia, fractionated small plugs must be examined with attention to explore polymetallic and other type of mineral deposits.
Organic geochemistry and palynology of Lower Cretaceous Zuunbayan oil shales, Mongolia
Masanobu YAMAMOTO(Mineral and Fuel Resources Department, GSJ), Delegiin BAT-ERDENE(Institute of Geology and Mineral Resources of Mongolia), Pureyiin ULZIIKHISHIG(Institute of Geology and Mineral Resources of Mongolia), Yoshio WATANABE(Mineral and Fuel Resources Department, GSJ), Noboru IMAI(Geochemistry Department, GSJ), Yoshiteru KAJIWARA(Japan Petroleum Exploration Co. Ltd.), Nobuyori TAKEDA(Japan Petroleum Exploration Co. Ltd.) and Terumasa NAKAJIMA(Mineral and Fuel Resources Department, GSJ)
1998
vol. 49 (6) P. 257-274
14 figs., 4 tables
Keywords: organic geochemistry, palynology, early Cretaceous, the Zuunbayan (Dsunbayan) Group, oil shale, Mongolia, paleoenvironment, biomarker
Abstract: Biomarkers and spore-pollens were analyzed for twenty-six oil shales from the Zuunbayan Group, Lower Cretaceous lacustrine sedimentary sequences in eastern Mongolia.
The distributions of n-alkane, steranes, hopanes, gammacerane and gammacer-2-ene indicate diversity in the contributions of an autotrophic prokaryote such as a cyanobacterium, nonmarine algae, terrestrial higher plants, heterotrophic bacteria and bacterivorous ciliates. The presence of thermally unstable compounds and low concentrations of diagenetically-generated compounds indicate that the samples are in an immature stage below the oil generation window.
Good correlations exist among organic carbon content, oil yield, bitumen content and n-heptadecane anomaly {2×n-C17/(n-C16＋n-C18) n-alkane ratio}. This indicates that the organic carbon content and oil yield was related to the contribution of a blooming autotrophic prokaryote which sourced the dominant n-heptadecane.
High C/S ratio of the samples and the low concentration of organic sulfur compounds indicate that the Zuunbayan oil shales were deposited in a freshwater environment. A palynological analysis shows a common assemblage of the Neocomian sediments belonging to the Boreal palynofloral Province. The detailed assemblage suggests that the area where the Zuunbayan oil shales were deposited was situated near the border between warm-humid and hot-arid climate zones. Although Mongolia was situated in midlatitude during early Cretaceous, the tropical-subtropical climate promoted thermal stratification and therefore bottom water anoxia in the freshwater lakes. The degree of development of bottom anoxia was likely controlled by nutrient supply from the surrounding area.
Extraction of clay mineral alteration zone in eastern Mongolia using JERS-1 data
Takashi OOKA(Technical Development Department, Metal Mining Agency of Japan), Hideya METSUGI(Technical Development Department, Metal Mining Agency of Japan), Manabu KAKU(Earth Remote Sensing Data Analysis Center) and Kazuhiro ADACHI(Mitsui Mineral Development Engineering Co., Ltd.)
1998
vol. 49 (6) P. 275-290
10 figs., 1 table
Keywords: JERS-1, Gobi, Shuteen, Ikh-Shankhai, Serven-Sukhait, Mongolia
Abstract: The Metal Mining Agency of Japan has been empowered for the examination and evaluation of effectiveness of JERS-1 data since 1993. The eastern Mongolia was selected as a case of semi-arid area for the evaluation. The object area is located in the eastern part of the Govi Desert spreading out from south of Mongolia, close to the border with China. Ikh-Shankhai, Shuteen and Serven-Sukhait are known for presence of porphyry copper type mineralization formed by small granitic intrusive rocks. JERS-1 OPS (OPtical Sensor) with some conservative technique of remote sensing was applied to identify the mineralization zone in this area. The findings of this study are as follows: (1) Based on the interpretation of color composite image (BGR=128), the silisification zone around the Shuteen mineralization zone has been identified by peculiar bright red brown color. This spectrum anomaly suggests that the minerals having absorption in band 1 and band 2, such as iron oxide, are distributed on the surface of the area. Photogeologically, this spectrum anomaly zone is interpreted as topographically high elevation area, and erosion resistivity is inferred to be extremely high as compared to circumferential rocks. These results agree with existing information that iron-silisified rock is distributed over the center of the mineralization zone. (2) There is the possibility that mineralization is distributed over the Ulgen area, because spectrum anomaly of the Shuteen area is very similar to that of the Ulgen area.
Preliminary study on the characteristics of Tsagaan tsakhir uul gold deposit, Bayankhongor, southern Mongolia
Sereenen JARGALAN(Department of Geochemistry, Graduate School of Science) and Satoshi MURAO(Mineral and Fuel Resources Department, GSJ)
1998
vol. 49 (6) P. 291-298
6 figs., 2 tables
Keywords: gold, epithermal deposit, mesothermal deposit, fluid inclusion, Tsgaan tsakhir uul, Bayankhongor, Mongolia
Abstract: The Tsagaan tsakhir uul gold deposit is located at the southeastern part of the Bayankhongor metallogenic zone, Mongolia, and is highly prospective for gold mineralization. The mineralized area is composed of Proterozoic migmatized limestone and marble-bearing schists, Early Cambrian biotite or two-mica granodiorites, and small dioritic stocks of Late Carboniferous age. Small number of NE-striking dykes of diorites, aplites, pegmatites, and quartz porphyries are also distributed in the area cutting Cambrian granodiorites. Gold mineralization is represented by several localities of quartz veinsets and veinlet zones, occurring both in Cambrian granodiorites and Proterozoic migmatized schists. Wall rock alteration is developed weakly as silicification, sericitization, albitization, chloritization and pyritization. In the area three types of quartz veins are observed: (1) metamorphic quartz veins; (2) mesothermal quartz veins; (3) epithermal quartz veins. Mesothermal quartz veins are richest in gold content. Within mesothermal veins gold is often associated with pyrite, chalcopyrite, galena and is also found as free grains in quartz. Gold content in quartz veins show a wide range between 0.1 and 749.6 g/t. Gold grains are bright to golden yellow in color and has grain size of 0.1mm to 3.0mm. The fineness of gold (1000Au/Au+Ag+impurities) varies from 830 to 940 giving an average value of 900. Most of the fluid inclusions observed in quartz are two phase L>V and range between 0.3μm and 10μm in size. The homogenization temperature of mesothermal veins ranges from 160℃ to 356℃. Not many facts are known for the epithermal veins in this district but our study has indicated that the homogenization temperatures of the quartz vein range from 107℃ to 120℃. The apparent salinity of fluid inclusions in mesothermal quartz ranges between 1.74 and 6.74 wt.% NaCl equiv, with an average 4.18 wt.% NaCl equiv. Based on this preliminary study, we have concluded that at Tsagaan Tsahir Uul the mineralizing fluid for mesothermal system was CO2-bearing and of low salinity, and that effective deposition of gold within the system happened at temperatures from 160℃ to 260℃, although the obtained temperatures show wider range.
Previous studies on the Erdenetiin ovoo porphyry copper-molybdenum deposit, Mongolia
Gunchingin DEJIDMAA(MONRUD Co., Ltd.) and Kazuki NAITO(Mineral and Fuel Resources Department, GSJ)
1998
vol. 49 (6) P. 299-308
5 figs.
Keywords: Erdenetiin ovoo deposit, Erdenet Complex, porphyry copper, Selenge Complex, Mongolia
Abstract: The Erdenetiin ovoo deposit in the Bulgan Aimag of Mongolia is the largest copper producer of the nation. According to the information available, the deposit is of porphyry type and controlled by complicated combination of structure, magmatic and geochemical factors. In the mineralized area widely outcropped are two types pf porhyryies: (1) Selenge Comple of Permian time (270-240 Ma) and (2) Triassic Erdenet Complex. The mineralization is related genetically and spatially to the Erdenet Complex. Sericite alteration of the deposit shows the K-Ar age between 210 and 190 Ma. The ore-bearing porphyries intruded rhythmically into the Selenge Complex. Sulfur isotopic compositions of sulfides exhibit bimodal distribution but satisfactory explanation for this phenomenon has not proposed yet.
Fluorite deposits in Mongolia：an outline
Jargalyn LKHAMSUREN(Mongolian Technical University) and Satoshi HAMASAKI(Mineral and Fuel Resources Department, GSJ)
1998
vol. 49 (6) P. 309-318
5 figs., 3 tables
Keywords: Fluorite deposits, Mongolia, eastern and central parts, hydrothermal type, volcanic rocks, plutonic rocks
Abstract: Fluorite is one of the leading economic minerals the same as copper, molybdenum, gold and coal in Mongolia. The reserve of fluorite in Mongolia ranks fifth in the world. There are more than 600 fluorite deposits in Mongolia. Especially eastern and central parts of Mongolia are important for economical fluorite deposits. Most of the fluorite deposits in Mongolia are hydrothermal type, and can be divided into two groups by their genetical relation to magmatic rocks. One group has relation to volcanic rock, and the other to plutonic rock. The former is classified in epithermal fluorite deposit and fluorite deposit in carbonatite host. The latter is classified in bertrandite-phenacite-fluorite, albitite, Mo/Sn-W and pegmatite deposit. The total annual production of fluorite reached 527,000 t in 1995. At present Bor-Ondor, Adag, Bujgar, Zuun-Tsagaan-Del, Tsagaan-Elgen, Orgon and Delgerkhaan deposits are in commercial production, and further exploration is being carried out. Bor-Ondor is the biggest mining and processing complex.
A manual of Romanization of Mongolian geographical terms
Renzo NUKUSINA(Tokyo University of Foreign Studies)
1998
vol. 49 (6) P. 319-340
7 tables
