(Presented as a public service of the china–resources.net web–site.)
Version: January 18th, 2026
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By
Minira B. Batkibetkova and Tamara Sh. Djunushalieva
Scientific Research Institute and Department of Chemistry,
Kyrgyz Technical University,
Bishkek, Kyrgyz Republic
Lecture was presented at Denver Mining Club Luncheon Meeting, held on 28 June 2004
Kyrgyz Republic, known also as Kyrgyzstan, with a population of about 5 million people, is located in Central Asia. It borders on the north with Kazakhstan, on the east with China, on the south with Tajikistan, and on the west with Uzbekistan.
Most of Kyrgyzstan is mountainous, covering about 76,460 sq. mi. (or 197,946 sq. km) with elevations up to 15,928 ft (or 4,855 m.a.s.l.).
The country is a major producer of gold and hydroelectric energy, with growing agriculture and food processing, manufacturing, and tourism. In 2002, the country’s main exports were gold, mercury, antimony, tobacco, cotton, fruits and vegetables and textiles, and major imports were oil, gas, iron, chemicals, pharmaceuticals, and machinery.
Geology of the Tien Shan Mountains, including that part within Kyrgyzstan, is extremely complex. As in Uzbekistan, with Muruntau the world’s largest gold mine and also in Kyrgyzstan there are several gold deposits with Kumtor the largest one. Canadian Cameco Corp., owning one-third of the equity interest, operates Kumtor Gold Mine and Processing Plant. Detailed information pertaining to Kumtor’s deposit geology, ore reserves, gold content, investment capital, development timing, mining equipment and operations, and production rates, can be found in E&MJ Sept. 1998 issue.
Kumtor floats its ore, consisting primarily of gold-bearing pyrite into concentration, which is reground and cyanide leached in a CIL circuit for 63 hours. However, since an accidental discharge of 20 metric tons of sodium cyanide into the Barskoon River, in May 1998, further use of cyanide leaching in Kyrgyzstan became extremely sensitive, and because of the accident is strongly opposed.
Considering the latter accident and interrelated ecological disaster, particularly in Kyrgyzstan, and numerous other countries, the search for an alternative, ecologically safer technology for extracting of gold from refractory ore became imperative.
The subject of this presentation are preliminary results of the tests of thiourea (NH2)2CS leaching. Although this technology has been tested in various countries, for various reasons it is still not preferred for industrial operations.
The laboratory tests of this project used samples of gold-bearing ores and flotation concentrates from the Terekan deposit (averaging 8g Au/t), the Ishtamberdy deposit (averaging 8g Au/t), and Chapchana (averaging 10g Au/t), Ak-Jilga, Savoyardy, Terkasy, Nichke-Suu and other gold deposits, all of the Kyrgyz Republic. Tests were completed as an initial, partial fulfillment of the Research Project KP-877. International Scientific Technical Center (SITC) sponsors the project. The scope of the research of this project is scheduled for 3 years, specified in detail for each of 12 quarters.
The literature investigation revealed that in Kyrgyzstan, individual ore bodies are controlled by complex regional and local tectonics, and they are hosted in Precambrian age metasediments. Gold mineralization is associated with gold-bearing pyrite and almost always with at least several percent of arsenopyrite. This mineral association forms the refractory type ores.
The refractory gold-bearing ores in Kyrgyzstan are characterized by complex structure, extremely thin impregnations of gold encapsulated in sulfides, and by components unfavorable for recovery with cyanide leaching. Since similar type refractory gold-bearing ores occur also in many countries, considerable efforts were made to find competitively effective, environmentally safer than cyanide leaching, and economically feasible alternative technologies.
In this research, further literature investigation confirmed that there are numerous factors that control gold mineralization. Our own observation indicate that concentration of gold appears to occur in low temperature hydrous solutions, often associated with organogenic compounds, including asphaltenes, and asphaltic acids. Numerous experiments have proven that in the natural waters gold occurs in the chloride complexes [Au(OH)2Cl2]-. It has been also well proven that hydrocarbons and other forms of organic matter, including hydro-plankton, precipitate and concentrate gold.
Therefore, considering the importance and well-proven factors of the latter, in our research we intend to reverse said process for recovery of gold from its high concentration in the gold-bearing ores. For this, we intend to apply similar processes, which occur in the nature for concentration of gold. In this case, in order to avoid detrimental impact on nature and to minimize potential health hazards, for extraction of gold from ore in the ore processing technology, we have initially tested and intend to continue research on recovery of gold from flotation concentrates, using instead synthetic chemicals and their equivalents, but made out of natural components.
In this lecture and of its summary are presented preliminary results of the laboratory tests of gold recovery from its flotation concentrates using humic salts and thiourea (NH2)2CS. Tested were samples from the Terekan gold deposit, which included three type of mineralization including: quartz with an insignificant amount of partly oxidized sulfides; arsenopyrite-pyrite sulfides, at higher horizons of the orebody, partly oxidized; and antimony-pyrrhotite sulfides, at higher horizons oxidized. The grain size of gold in sulfides ranges from a few to 750 microns. Larger grains occur in quartz veins. The Terkan deposit contains typical refractory ore.
Although being familiar with various combinations of the cyanide-based technologies, among other non-toxic technologies applicable for gold recovery, thiourea appears to be most effective. It proceeds according to the following chemical process: Au+CS(NH2)2 + X+n(H2O2H+) Au [CS(NH2)2]2+ Xn-1.
Using thiourea, our laboratory tests on the refractory ore proved 83 to 86% recovery of gold from its flotation concentrates. This process is effective in ambient temperature conditions.
The above summarized gold recovery approach from the refractory type ore, among others, appears to be strongly supported by a recently published paper on “Leaching of noble metals from ores by thiourea” authored by Barbara Kolodziej (Physicochemical Problems on Mineral Processing, No. 33, 1999; Institute of Inorganic Chemistry and Metallurgy of Trace Elements, Wroclaw Polytechnic, Wroclaw, Poland). She reports leaching results of the noble metals from carbonate-hosted gold-bearing mineralization, with 5g Au/t, of which flotation concentrate contains 100g Au/t, in which gold is encapsulated in pyrite and arsenopyrite matrix. Furthermore, she reports that the application of thiourea for leaching of noble metals, from refractory type ore, is very effective. After 3 hours of leaching at 18oC, 92.5% and 92% of gold, platinum and palladium, respectively, was recovered. In the case of gold concentrate originating from said refractory ore, the preliminary reductive leaching was used. In the essential leaching by thiourea, a 47% increase of leaching of gold was observed. After 20 hours of leaching at 18oC, 68%, 98% and 99% of gold, platinum and palladium was leached out.
Note: This summary was prepared by Jan Krason (Geoexplorers International, Inc.; e-mail: geoexpl@geoexplorers.com or geoexpl@eazy.net or Phone: 303-759-2746), U.S. based collaborator in the SITC, KP-877 Project. He also added the reference to B. Kolodziej’s paper.