資源地質，66(2), 89 ～94, 2016 特集：モンゴルの鉱物資源

資源情報

Gold resources in Mongolia

by S. JARGALAN*

Abstract: Mongolia has considerable reserves and resources of gold in both placer and primary deposits. Gold has been mined in the country since ancient times, but recently it plays main role on country’s mining activity as well as economic development. Placer gold deposits are studied much and most of them are now under mining activity. Pri- mary gold deposits are studied weakly and only Boroo gold deposit is mined and other deposits are under development study level. Distribution of gold deposits and occurrences depends on mineralization type, but generally shows linear form along the independent geotectonic units, or bigger fault zone. The data of various geological reports of gold metallogenic and gold bearing belts of Mongolia suggest that there are 17 belts containing total amount of 2,100 tons of gold.

1. Introduction development study level. Geological background for the gold deposits is given in Mongolia has considerable reserves and resources of gold Jargalsaihan et al. (1996). Distribution of gold deposits and in both placer and primary deposits. Gold has been mined in occurrences depends on mineralization type, but generally the country since ancient times (Dejidmaa, 1996; Ochirbat, shows linear form along the independent geotectonic 1999), but recently it plays main role on country’s mining units, or bigger fault zone. According to general trend and activity as well as economic development. Placer gold distribution of gold deposits and occurrences, a number of deposits are studied much and most of them are now under potential gold metallogenic belts and gold-bearing belts are mining activity. Primary gold deposits are studied weakly and identified (Fig. 1). only Boroo gold deposit is mined and other deposits are under Gold mineralization took place, with varying intensity

Fig. 1 Distribution of gold deposits in Mongolia (Mineral resources map of Mongolia, 2002).

2015 年 8 月 3 日受付，同年 10 月 26 日受理 * Mongolian University of Science and Technology, Ulaanbaatar, Mongolia (Corresponding author, E-mail: [email protected]) Key words: gold, vein, porphyry, placer, fault-controlled, Boroo mine

89 90 S. JARGALAN 資源地質： in Neo Proterozoic, Early Cambrian, Early Paleozoic, with powerful machines and latest technology quickly Middle Paleozoic and Late Paleozoic, Early Mesozoic, grew into a modern settlement having all the needed social Late Mesozoic and Cenozoic metallogenic periods. The infrastructure. By 1990, there were two joint ventures intensity of mineralization increases from older to younger operating gold. One is Mongolian-Soviet Joint Venture age. Gold mineralization is represented by three economic “Mongolsovtsvetmet” in the Tolgoit gold district of North types: veins, mineralized zones and placers. Hentii gold belt, and another one is Mongolian-Bulgarian Joint Venture in the Bayanhongor gold belt. From 1974 to 2. Gold mining history 1990 these two Joint Venture companies produced total of 9084.8 kg of gold, from which 4183.95 kg were exported Historical records and archaeological findings suggest to the USSR (former) and Bulgaria. that the gold mining on the territory of Mongolia began 1990-Recent: There was big change on society and since ancient times. Before the establishment of the politics of Mongolia, in early 90’s. The country has Great Mongolian Empire in 12th century, the territory of embarked to a market economy, which caused much Mongolia was inhabited by numerous tribes and there is economic difficulties. To recover this economic crisis an evidence that they were extracting gold for jewelers Mongolian government made a decision to develop mining and, in some instances, to sue as pay off if defeated in of gold and initiated“ Gold-2000” program. According tribal conflicts. The scientific survey of gold deposits, to this program gold operating and mining activity has prospecting and estimation of reserves as well as industrial abruptly increased, and once it was a lot of mining; now mining of gold began only after the People’s Revolution there are almost 130 companies, engaged on this business. in 1921. The history of gold exploitation in the territory of Mongolia can be divided into 4 main stages: 1901-1921; 3. Distribution of gold 1939-1954; 1974-1990 and 1990-Recent. 1901-1921:First stage of gold exploitation was conducted At present, in the territory of Mongolia a number of by Mongol-Or association on the Yeroo, Shariin Gol, potential gold metallogenic and gold-bearing belts are Haraa, Yamaat, Nyalkh, and Tolgoit river area at the North identified. The data of various geological reports of gold Khentei gold belt. At that time gold was mined mostly by metallogenic and gold bearing belts of Mongolia suggest foreign investors. In many cases, historical records reflect that there are 17 belts containing total amount of 2,100 facts of gold smuggling out of the country, therefore, it tons of gold. Seven of them are considered to be as high can be estimated that the total gold production was 9346.4 gold potential belts: North Khentii, Bayanhongor, Hangai, kg. In 1923, the Mongolian government issued the mining Jid, South Khentii, Ulziit, and Urgamal belts. Economic regulations which declared the land and underground deposits and potentially economic occurrences belong mineral resources should belong to people. In accordance mainly to the gold-sulfide-quartz and gold-quartz ore to this, all coal and gold mines were nationalized. formations. 1939-1954: Mongolian Government set up“ Mining and  The Northern Hentii belt occupies the territory of Mineral Resources Trust” which is charged for the task of Tov, Selenge, and Bulgan prefecture, covering total of surveying and exploring natural resources. That time gold 400km long and 30-100 km wide area (Fig. 2). This belt is mining was limited and there was small mines at the Boroo limited by two deep faults: Bayangol fault on its northern deposit of North Hentii gold belt and Bayanhongor gold border and Yoroo on its southern border. This belt can belt. Mining of placer gold deposit at the Bayanhongor be divided into five districts in terms of gold deposits, area started in 1939 and gold production reached 22.3kg in content and geological setting specifics: Zaamar, Yoroo, 1939; 38 kg in 1940; and 40.1 kg in 1941. It continued for Boroo, Tsaidam and Tseel. Geologically this belt is studied 15 years and altogether 695.4 kg of gold was produced. In well and the most of gold mining activity is in progress the Boroo area during 1943-1954 gold mining operation there. The belt contains well-known big deposits like was carried out on auriferous quartz veins and the Narantolgoi, Sujigtei, Boroo and Bumbat (Fig.2). production was 20000 m3 ore and 300 kg of gold.  The Bayanhongor belt is second biggest after the 1974-1990: Gold mining sector received a strong impulse North Hentii in terms of its potentiality, and locates at by setting up the first Mongolian-Soviet Union Joint the western part of central Mongolia, occupying territory Venture at the Tolgoit placer deposit. The mine equipped of Bayanhongor prefecture. It is 250 km in length and 66(2), 2016 Gold resources in Mongolia 91

Fig. 2 Geologic outline of the western Hentii belt.

60-90 km in width. This belt is characterized by wide The belt consists of wide spread rocks of volcanogeno- spread rocks of volcanogeno-sedimentary, sedimentary, sedimentary, sedimentary, and metamorphic rocks metamorphic and magmatic rocks. The belt can be divided intruded by Paleozoic and Mesozoic granitoids. This into 2 main zones: Baidrag river and Tuin river basins. belt can be divided into 4 gold bearing districts: Balj gol, Most prospected and operating deposits are located in the Terelj, Modot, and Janchivlan. Balj gol district is direct Baidrag river basin, Burd valley and Jargalant mountainous continuation of gold belt in Russia. Terelj district has range . several placer gold deposits and some of them are mined The Jid gold-bearing belt is located almost in the most in 1902-1910 years. Modot district is characterized by northern part of Mongolia near the boundary of Russia. auriferous quartz veins and sulfidized veinlets. This is The territory of this belt is occupied by deep forests and known for tin and tungsten mineralization. There are because of its improper road network the area was not several placer deposits in Janchivlan district and the mining surveyed properly. The belt is composed of variable rocks of activity has started since 1990. volcanogenic, sedimentary, metamorphic, intrusive and dike  The Ulziit belt occupies territory of Omnogobi rocks. Gold mineralization occurs in quartz veins, skarns, and Dundgobi prefectures. The area of this belt is not greisens and sulfidized zones and they associated with silver, economically utilized and has limited reserves of water copper mineralization. There are some gold containing and fuel. The belt is composed of rocks of sedimentary, tungsten, molybdenum and lead zinc mineralizations. volcano-sedimentary and volcanogenic rocks. There are The South Hentii belt is located at the central part of some positive perspectives to discover primary ore of gold. Mongolia, and has considerably good economical and The Hangai belt is located at the Hangai mountainous geographical conditions comparing to the other gold belts. range, occupying the territory of Arhangai, Ovorhangai ad 92 S. JARGALAN 資源地質：

Zavhan prefectures. There are some placer gold deposits in found in the deposit area. Seven large veins are 100-800 the valley of the mountainous range. Recently one big gold m in length, with average thickness ranging from 0.8 m to placer has been discovered in the valley of Khavtsgait, Olt, 3.2 m. These are identified down to 100-200m in depth. Zuun Sodot and Baruun Sodot. Average gold content ranges from 7 to 30 g/ton.  Tavt deposit of Jid metallogenic belt is located 200 4. Types of gold deposit km north-west from copper deposit Erdenet. The area is composed of Vendian-Lower Cambrian metamorphic The known deposits of Mongolia are represented by volcanogenic-sedimentary rocks and Permian-Early three economic types: veins, mineralized zones and placers. Triassic intrusive body. These formations were intruded by several Triassic-Early Jurassic dikes. About 100 auriferous 4.1. Vein deposits quartz veins were found. Length of veins vary from 100 Vein-type deposits are the most developed one, while to 600 m with thickness from a few centimeter up to 8.5 the bulk of proven reserves is associated with placers. m. Content of gold ranges from 7 g/ton to 14g/ton. Gold The considerable part of the vein type deposit belongs to is constantly associated with silver ranges of 30-60 g/ton, economic and potentially economic targets. Here we will copper 0.8-1.6 g/ton, and molybdenum 0.1-0.3g/ton. state some brief characteristics of main vein deposits. Brief Tsagaan Tsahir Uul deposit is located 700 km southwest description of main vein type deposits are characterized from Ulaanbaatar. The deposit area is composed of below. Proterozoic metamorphic rock, Proterozoic granitic body Narantolgoi deposit is situated 90 km north from capital and Permian dioritic stock, intruded by quartz porphyry, Ulaanbaatar in the North Hentii gold metallogenic belt. and lamprophyre dikes. The deposit is represented several The deposit area is composed of Lower Paleozoic flyschoid localities of quartz veins and veinlet zones. Veins stretch up sequences, Late Paleozoic granitic body and Devonian to 1000m and continues to 200 m in the depth with 0.1 to volcanic rock. Gold mineralization is represented by 0.5 m thickness. Wall rock alteration is developed weakly as several quartz veins distributed at the endocontact part silicification, pyritization and sericitization. Gold content of of granitic body. The main vein was traced for 2200 m quartz veins range from 0.1 g/ton to 746 g/ton. along the striking and 370 m in depth. Its thickness ranges Urliin ovoo deposit is located at the Dornot volcano- from 0.1 m to 3.5 m. Some other veins are situated in the tectonic structure of Eastern Mongolia. The area is hanging wall of the main vein. These veins are traced composed of Proterozoic granite-gneiss, Lower Paleozoic 1200 m along their striking 150 m in the depth. Gold ore granodiorite body, intruded by many dykes of aplite, is characterized by massive and impregnated structures. pegmatite, microdiorite, rhyolite, lamprophyre and diorite- Gold is major mining component. Content of gold in veins porphyry. The gold mineralization is related to quartz ranges from 5.7 to 19.2 g/t and silver is up to 30 g/t. veins and hydrothermal metasomatic alteration zone. Gold Tsagaan Chuluut and Sujigtei deposits are situated content ranges from 0.1 g/t to 30 g/t. The main ore minerals near the Narantolgoi deposit in the same gold belt. Tsagaan are gold, pyrite, chalcopyrite and bornite. Chuluut is presented by practically one quartz vein that is 4.2. Deposits of mineralized zones 220 m long situated at the marginal part of granitic body. The auriferous vein was traced to 160m in depth with  Boroo deposit (Fig.2) is situated 100 km north from average thickness of 10m. Average gold content is 14.8 Ulaanbaatar. The gold mineralization is associated with g/t. The Sujigtei deposit is located in the fault zone and zones of intensive hydrothermal alteration. The deposit represented by the some several auriferous quartz veins. area is composed of Lower Paleozoic meta-sandstones and The biggest one is 170 m in length and average thickness is meta-siltstones, Late Permian-Early Triassic leucocratic 0.48m. Gold content of these veins range from 10 g/ton to biotite granite, intruded by many dikes of intermediate and 25 g/ton. basic composition. The mineralized zone is characterized  Bumbat deposit is located at the Zaamar district by chloritization, albitization and beresitization , which is of North Hentii gold metallogenic belt. The deposit commonly seen in Russia and Mongolia, composed of quartz, area is composed of Lower Paleozoic metasandstones pyrite, Kf and mica. and metasiltstones, intruded by numerous basic and The ore bodies are 250-350 m in length and they are intermediate dikes. About 100 quartz veins have been traced to 250-350 m in the depth. Thickness of ore bodies 66(2), 2016 Gold resources in Mongolia 93

Fig. 3 Distribution gold mineralization types in Mongolia.

is more than 10 m. Gold is the principal useful component, gold grains often occurs along the fissures, and it is also which is associated with copper, lead and iron sulfides. found in the altered host rock. Gold content ranges from 1 Two natural types of primary ores and oxidized ores are g/ton to 32.8 g/ton. recognized. Geotechnical conditions of the deposits are 4.3. Placer deposits favorable and allow to work with it by open-pit mining method to depth 150 m deep. Economic gold placers are mostly located at the  Hoh bulagiin hondii is located at the Bayanhongor North Hentii, Bayanhongor, Hangai and South Hentii gold metallogenic belt. It is skarn type mineralization. The metallogenic belts. A series of minor placers were deposit area is composed from Proterozoic metamorphic discovered in the Mongolian Altai, Hovsgol, and Sourthern unit intruded by Carboniferous granitic body. The primary Mongolia. Commercial gold potential is associated with mineralization is situated at the contact between granitic Quarternary sediments with a lesser extend of Upper body and layer of limestone of Proterozoic metamorphic Neogene sediments. Placers are fed by gold derived from unit. There are 5 zones of skarn mineralization. The primary ore source of various types of gold mineralization. skarn is composed of clinopyroxene-garnet skarn with The greater part of placer gold is concentrated in the flood- disseminated chalcopyrite, bismuth, arsenopyrite, plains and terraces of recent rivers. sphalerite, enargite and cubanite. The primary gold-skarn Zaamar district of North Hentii gold belt is the biggest ore recognized to be related to hydrothermal metasomatic region in the country and situated in the drainage basin of process. river Tuul. This area was first discovered during geological Olon ovoot deposit is located in the Ulziit metallogenic mapping in 1978-1982y. Geographic and economic belt about 13 km south east of Mushigai hudag rare earth condition of the district is favorable for mining activity. At element deposit. The deposit area is consists of Silurian the Zaamar district numerous gold placers were found and sandstones, siltstones and shales and Devonian gabbroic now more than 40 private and governmental companies are and dioritic bodies. Main alterations were observed as operating on the placer gold. sericitization, pyritization, argillization and silicification The area is composed of Upper Cambrian metasediman- containing auriferous quartz veins. Dendrite shaped native tary rocks, Carboniferous-Permian sandstones, siltstones 94 S. JARGALAN 資源地質： and Upper Triassic-Lower Cretaceous sedimentary rocks. contained at the base of loose sediments. Gold grains are Devonian granitic bodies and early Mesozoic dikes are comparatively coarse. distributed. In the Zaamar district two types of economic Yalbag group deposit situated 50 km south from Tolgoit placer deposits are found: Placers along the river Tuul and mine and includes placers Yalbag, Berleg and Tsagaan placers on the right-bank tributaries. Chuluut. The Yalbag placer occurs in the flood-plain Placer along the river Tuul continues almost 40 kms. part of the same named valley and at the lower end it is It has a long and complex history of formation related to connected with Berleg placer, while at the upper end it is neotectonic regime of the country. A flood plain of river abutted by the Tsagaan Chuluut deposit. Tuul is 1 m high and 0.5-1.0 km wide and it consists of Buhlei group deposits are located north-west 70 km 6-8 m thick alluvial sediments. It has 5 terrace on its right- from Tolgoit mine and includes Ulent, Tsamhag and bank. Both alluvial sediments both of flood plain and all Harganat placers. The Ulent deposit is the largest and terraces have gold bearing predominantly gravelly horizon. situated at the Ulent river valley. Main gold content is All right-bank valleys of river Tuul contains placer gold discovered at the base of alluvial sediments. deposit. The large ones of them are Hailaast, Bayangol, Shariin gol group deposit is situated at the southwest Tsagaan bulag, Toson and Ar-Naimgan. of Yoroo gol group deposit. This group contains deposits The Hailaast placer, the most richest one, locates at the named Shariin gol, Burhant, Havchuu and Ovoljoo. A Hailaast valley on the right-bank tributary of Tuul deposit. considerable part of gold is concentrated in the shallow The total length of the valley is 14 km, and width range of placers. Size of gold grains range from 0.56 mm to 1.25 300-500 m. Two main streaks are defined in the Hailaast mm, and fineness is 860-904. valley, from which the lower one is near the bedrock. Placers of Bayanhongor belt are located 60-30 km Gold grains in placer are coarse and medium in size. The northwest of Bayanhongor town. The area is composed fineness of tabular and sheet like grains are mostly 899. of Archean to Proterozoic metamorphic rocks, Lower Yoroo gol district of North Hentii gold belt is located Cambrian ophiolite complex, Proterozoic granitic at the northern part of Mongolia, near boundary batholiths and Permian dioritic and granodioritic stocks. of Russia. The area is composed of Precambriam There are several group of placer deposits at the Jargalant sedimentary-metamorphic rocks, Devonian terrigenous Mountain range, Baidrag river basin and Bombogor area. and volcanogenic sequences, Jurassic and Cretaceous The Jargalant group of the placer deposits is the biggest continental molasses. Early Paleozoic, Devonian and Late and richest one and located at the dry valley drainage. It Permian granitoids and gabbro-granite associations are includes Muhar-ereg, Ovor chuluut, Sairiin hudag and Ar distributed. More than 40 gold deposits within 7 groups of chuluut placers, which were mined during 1939-1954 and placers were found in this district. have been mined since 1990. Bugantai group placer deposit have a long history of development and main resource of Tolgoit placer mine. The Tolgoit placer had been mined during 1910-1917 References and have been mining since 1974. This group includes Dejidmaa, G. (1996) Gold metallogeny of Mongolia. Nariin, Sangiin, Baga Ulent, Ih Ulent Namag placers. Mongolian Geoscientist, no. 1, p. 6–29. The economic gold concentrations are associated mainly Jargalsaihan, D., Kazmer, M., Baras, Z. and Sanjaadorj, D. with lower horizon of waterlogged Pleistocene alluvial (1996) Guide to the geology and mineral resources of sediment. Gold grains are generally 0.1-10 mm in size, but Mongolia, 330 p. there was found nugget weighing up to 3.0 kg. Ochirbat, P. (1999) Development strategy of the precious Yoroo gol group placer located 20 km south of Tolgoit mineral complex and ecology of Mongolia (in mine includes Yoroo, Ih Ajir, Baga Ajir placers. Gold is Mongolian). 391 p.