Replacement texture of cerussite by galena and hydrocerussite with differrent mode of occurrences are found in the reaction products of cerussite with Na₂S hydrothermal solution at temperature from 130 to 170 °C. Whereas galena crystals occur mainly on and near the cerussite surfaces, hydrocerussites are found at the inside of cerussite-galena boundaries as replacement. This different modes of occurrences are well explained by the isolation of hydrothermal solution at/near the cerussite surfaces by the covering and growth of galena over cerussite. While galena crystals are deposited from the open solution enriched in sodium and sulfides, hydrocerussite are formed from the isolated solutions which are enriched in lead and carbonate under the effect of progressive dissolution of cerussite. Such isolation of solution by the covering and growth would be important for making the variation of mineral assemblages with various replacement textures under natural hydrothermal conditions.

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Mongolia is one of the major copper producing countries in Asia. Currently two world class porphyry copper mines, Erdenet and Oyu Tolgoi mines, are in operation and Tsgaan Tuvarga mine is under construction. In 2013, two operating mines produced 650kt of copper concentrates and exported them to China, which earned 45% of foreign currency of Mongolia to underpin its economy. The Oyu Tolgoi mine which started operation in 2013 and is scheduled to be expanded its production up to 531kt/y in few years. Shipping of concentrates is now targeted to China, however new market such as Japan and Korea is also considered. From now on, it is necessary to observe the production and export trends of Mongolian copper concentrates.

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Mongolia has considerable copper reserves allowed for the country to set up a new subsector of mining industry. Main parts of Mongolian copper reserves are detected in the porphyry copper-molybdenum and copper-gold typed deposits. Erdenet mine and Tsagaan Suvarga ore deposit represent the former, and Oyu Tolgoi mine does the latter. While a great number of other copper occurrences are distributed over the country, Oyu Tolgoi mine opened in 2013 achieves world-class copper reserves. Copper industry in Mongolia is characterized by the productions of copper concentrates in Erdenet and Oyu Tolgoi mines and cathode copper by SX-EW as Solvent Extraction and Electro-winning at Erdenet mine. Copper wires and electrical cables are only domestic products in Mongolia, and the exportation to foreign countries, like China, has not been implemented due to a lower competitiveness in their prices.

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It could be said that Mongolia, like countries in Indochina, is a frontier in terms of rich mineral resources that are left unexplored in Asia. JMEC hosted a training program called “Training on Geological Survey in Foreign Mining Sites (Mongolia Geological Excursion).” The training program targeted young engineers working for mining companies. This excursion party visited not only the Erdenet porphyry copper mine, but the Bayangol iron mine, the Khotol limestone mine, the Boroo gold mine, and the Zamaar alluvial gold district.
Type of gold deposits in Japan are mainly hydrothermal type, but the Boroo mine is an Orogenic type gold deposit where gold ore occurred in the fracture zones and granites in its lower fault. Meanwhile, the Zamaar gold deposit is a large-sized placer type gold deposit that extends into the valleys on the north-west slope of the Zamaar Mountains and Tuul river itself on the west side of the Zamaar mountains. Au reserve of Zamaar alluvial gold district has more than 200t and Au grade is 1.5g/m3 of sand gravel ore. This alluvial gold deposit has a relationship with auriferous quartz veins (NE-SW) which intersect at a right angle to the most of valleys. There are more than 1000 quartz veins(0.1-40ppm Au) are known and one of largest vein, Bumbat vein has average Au content of 3.9ppm and Au reserve of 0.5t. The Zamaar alluvial gold district is very impressive in terms of mining method and mining scale, etc.

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The 14th Chilean geological congress was held at La Serena in October 4th to 8th, 2015. A short report on the congress, particularly on economic geology session, is presented here for Resource Geology members.

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A future perspective of the supply of mineral resources is discussed on the basis of the example of rare earth elements (REE). Rare earth elements have been produced from monazite, bastnäsite, and ionic clay ores mostly in China during the last two decades. However, Chinese resource nationalism over the production and export has made the supply of REE unstable in terms of price and quantity. A possible alternative REE source is phosphate ores, which contain a few amount of REE as impurities with some toxic and radioactive elements. Despite low in REE concentration in phosphate ores, more than 300,000 tons of REE (as oxides), which correspond to more than two times of present-day REE demand in the world, are included in the ores annually produced from the mines for fertilizer production. The recovery of REE with other impurities from phosphate ores is beneficial not only to produce REE but also to avoid pollution in farming lands. While our society shifts from the plundering one to the sustainable one, in which mineral resources would be completely recycled, it is desired to recover all the by-product elements from the major ores in order to decrease the impacts on the environment and trigger innovations in the manufacturing industry.

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