Thailand trip to Chatree Gold Mine and Padaeng Zinc Mine (Wed, Oct 17, 2007)
Trip to Chatree Gold Mine & Padaeng Zinc Mine
Click for PDF of results of the trip
In October 2007, the Hong Kong Branch arranged a 4-day visit to two opencast mining operations in Thailand, the Chatree Gold Mine, located in north- central Thailand, and the Padaeng Zinc Mine, located in north-western Thailand, close to the Padaeng Zinc Mine border with Myanmar. Nineteen professionals joined the trip.
The main party from Hong Kong arrived in Bangkok after midnight and, with only 4 to 5 hours of sleep, had to return to the airport by 6:30am on the 18th October to catch the early morning flight to Sukhothai in the north. The subsequent road journey from Sukhothai Airport to the Chatree Gold Zinc Mine in nearby Phichit Province took 2 hours.
Upon arrival at Chatree, we were welcomed by Mr. Phil MacIntyre, the mine manager, and his staff who provided us with briefings on the development history of the mine, the local geology, an overview of the mining and processing operations, and the company’s exploration strategy for the future development of the mine. These briefings were followed by a most welcome lunch, our first meal of the day having foregone breakfast because of the early morning flight from Bangkok. After lunch, Mr. Suphanit Suphananthi, the mine’s Geology Manager, and Mr. Guy Davies, the Mining Manager, led a conducted tour of one of the pits and the processing plant. The group left Chatree late in the afternoon, returning to Sukhothai to spend the night.
History
The Chatree Gold Mine, situated 280 km north of Bangkok, is owned by the Australian mining company, Kingsgate Consolidated Limited, and operated by its wholly owned subsidiary, Akara Mining Co. Ltd. Production commenced at the mine in November 2001, and in 2003 the processing plant was expanded to increase ore throughput to approximately 2 million tons per year. In 2006, the
mine produced approximately 140,000 ounces of gold and 450,000 ounces of silver. At the time of our visit, it was estimated that the existing ore deposits would be exhausted within 9 to 12 months. In anticipation of this, the mining company had been carrying out extensive investigations in the area to The initial briefing at the Chatree Gold Mine Location of the Chatree Gold Mine and Padaeng
Zinc Mine The Padaeng Zinc Mine The Chatree Gold Mine the north of the present main pits. The company is now awaiting approval from the Thai Government for the northern mine lease, which will guarantee the long-term future of the mine.
Geology
The Chatree Gold Mine is located within the Loei-Petchabun Volcanic Belt which extends from northern Laos southwards into central Thailand. In the Chatree area, this belt is oriented roughly north-south. The volcanic rocks are of Permo-Triassic age and include mainly andesites, dacites and rhyodacites. These are intercalated with volcanaclastic and epiclastic sediments, as well as limestones and marls. At the mine site, the rocks that host the gold/silver deposit include andesitic and dacitic tuffs and fine grained sedimentary rocks.
Mineralisation at Chatree is a low-sulphidation quartz carbonate adularia-style epithermal system, occurring in shallow to steeply dipping structures that carry gold-bearing veins, breccias, and stockworks.
Processing
Ore processing at Chatree involves a conventional carbon in leach process. Excavated ore from the pits is first reduced to 80% passing 95mm in a jaw crusher, and then passes into the milling circuit. Milling consists of one pass through a SAG mill followed by closed circuit grinding in a ball mill.
The resulting slurry, containing fine solids with approximately 80% passing 75µ, is then fed through hydrocyclone classifiers into the leaching circuit. The first leach tank acts as a lime/oxygen pre-conditioning tank, which aids in removing soluble iron from solution and reduces the reactivity of sulphides in order to lower cyanide consumption. After pre-conditioning, cyanide is added to leach the gold and silver, which is then adsorbed onto activated carbon grains.
Gold and silver are removed from the carbon in the desorption circuit under high temperature and in the presence of cyanide and caustic. The carbon is regenerated and returned to the leaching circuit for re-use. The gold/silver rich solution is passed through electro-winning cells where the metals are deposited on steel wool cathodes. These deposits are filtered and dried and then smelted in a gas furnace before pouring into gold/silver bars. The bars are shipped to a refinery in Hong Kong for final separation into saleable gold and silver. Tailings from the carbon in leach circuit are pumped though a two stage cyanide detoxification circuit, where the cyanide content is reduced to acceptable levels for disposal in the lined tailings storage facility. The facility operates in closed circuit with the processing plant, decanted water being returned to the plant for re-use.
Environmental Issues
Chatree carries out a comprehensive environmental auditing and review programme to assess compliance with licence conditions, relevant legislation, Environmental management System Chatree Pit C Members of the Hong Kong Branch at the Chatree processing plant objectives and best practice environmental management. The programme is based on regular internal and external environmental audits which are regarded as key feedback and quality control mechanisms that facilitate continual improvement of environmental management programmes and systems.
PADAENG ZINC MINE
After breakfast on the morning of the 19th, we left Sukhothai for the 3 hour drive to Mae Sot on the Thai-Myanmar border. Upon arrival at the Mae Sot mine site we were welcomed by the mine manager, Mr. Tianchai Singhakharn, and his staff who joined us for lunch. After lunch, Mr. Tianchai gave us a detailed briefing on the history of the company, the history of the mine itself, an overview of the
processing at Mae Sot, and an outline of the company’s various community initiatives. Following the briefing, Mr. Ronnachai
Lianghiranthawon, one of the mine’s senior members of staff, led a conducted tour of the pit and the processing plant. We left the mine late in the afternoon, to spend the night at a hotel in Mae Sot.
History
Leases to mine the Padaeng zinc deposit were first granted by the Thai government in 1972 to the Thai Zinc Company. Then in 1982, the government granted a 25-year concession to the Padaeng Industry Public Co. Ltd. for further exploitation of the deposits. In 2006, the mine extracted more than 500,000 tons of ore, from which just under 100,000 tons of concentrate and 60,000 tons of high-grade ore were produced and sent to the company’s smelter at Tak for final processing. Unfortunately, at the time of our visit, mining operations had been suspended temporarily, awaiting renewal of the mining licences for critical portions of the mine property which, when granted, will enable mining operations to resume.
Geology
The Padaeng zinc deposit being exploited at the Mae Sot mine is a non-sulphide deposit thought to have been derived from a body of earlier zinc sulphide mineralisation that accompanied tectonic activity during the Cretaceous (Reynolds et al., 2003). It is postulated that zinc-bearing acidic supergene fluids, generated by oxidation of the precursor sulphide body, reacted with carbonates in the underlying Jurassic rocks. These fluids, which were channelled downwards by permeable dolomitic sandstones and by steep fracture and fault zones, promoted deep weathering and karst formation, allowing mineralisation to extend down dip for at least 150 m. The precursor sulphide body has since been removed by erosion.
The Padaeng deposit, hosted by a mixed, deeply weathered, carbonate-clastic sequence of Middle Jurassic age, occurs in the hanging wall of the Padaeng fault, a major northwest-trending structure. The dominant non-sulphide zinc mineral in the deposit is hemimorphite with minor smithsonite and hydrozincite.
Processing
In the processing plant the low-grade, generally highly weathered, ore from the pit, with a zinc content of less than 10%, is passed through a washing drum for initial size segregation. Material of particle size >10mm is fed through a jaw crusher, whereas the coarser material with a particle size<10mm is fed through a spiral classifier. The product of these two processes then passes in to a
ball mill for further size reduction. Fine-grained milled material next enters a hydro cyclone separator to further concentrate the heavier metal-rich particles. The resulting slurry is fed into pre-conditioning tanks where additives, including sodium hexametaphosphate, sodium sulphide, stearyl amine and pine oil, are introduced to facilitate subsequent enrichment in the froth floatation cells. Concentrate from the floatation cells is thickened and dewatered, producing a damp, cake-like material with an average zinc content of approximately 27%. The concentrate is taken by road to the company’s smelter at the provincial capital of Tak where it is combined with higher grade concentrates imported from as far afield as South America. The combined concentrate is treated by acid leaching, filtration, and electo-
winning in the Tak smelter to produce the final zinc product.
Environmental Issues
Padaeng Industry Public Co. Ltd. attach great importance to environmental issues. At the Mae Sot mine site, the requirements specified in the company's environmental impact assessment report, as well as the standards promulgated by Thailand's Department of Primary Industries and Mines, are strictly followed. There is an ongoing programme of rehabilitation of waste dumps through topsoiling and revegetation using vetiver grass and native trees. Also, the tailings ponds, which are fully lined, have been designed with the capacity to cater for severe rainstorm conditions and the surface drainage systems around the mine site are designed to ensure that the amount of suspended solids in water courses leaving the site are within prescribed limits.
The party left Mae Sot on the morning of the 20th October for the airport at Sukhothai. En route, there was time for a brief stop-over to visit the ruins of the ancient palace at Sukhothai. The palace was the centre of the kingdom of Sukhothai, the first main Thai kingdom, which lasted from 1238 until the middle of the 14th Century. During its relatively brief period of pre-eminence the Sukhothai Kingdom is credited with having been the birthplace of both the Thai language and the Thai alphabet.
ACKNOWLEDGEMENTS
We wish to thank Kingsgate Consolidated Limited/Akara Mining Company Limited and Padaeng Industry Public Company Limited for giving us the opportunity to visit their mine sites. In particular we wish to thank Mr. Phil MacIntyre of Kingsgate and Mr. Tianchai Singhakharn of Padaeng, and their respective staff, both for their generous hospitality and for providing us with an informative insight into their impressive operations.