ALLUVIAL TIN MINING AND PROCESSING AT HEINDA MINE: A CHALLENGE FOR ENHANCING RECOVERY ALONG WITH BY-PRODUCT OF U-TH-REE IN MONAZITE

摘要

The Heinda mine is the biggest alluvial tin mine in Myanmar, located at 50 km east of Dawei, Tanintharyi. This mine is a quite well-known tin mine with a long history of exploration and mining since colonial time. Heinda mine was undertaken by several operators and most recently by Myanmar Pongpipat Co., Ltd (MPC), a Thailand Company. The last a couple years, due to uncertainty of the Myanmar government's policy as well as environment constraints and poor infrastructures, the production of the mine was in the range of only 100-300 tons/year. The Heinda concession covers an area of 8.23 sq.km. with an active mining area of 3 sq.km. approximately. The mine is characterized by hilly terrain with the highest peak at Hpolontaung. The mine is situated in an area with an 8 months annual rainy season.Geologically, it consists of mainly of alluvial tin deposits with some intercalations of eluvial mineralization, indicated by a significant proportion of gravels in the formations. Several episodes of deposition are separated into different distinct layers, namely overburden, A1, A2, B1, and B2 in descending order. In-situ tin resource is estimated at more than 50,000 tons at 0.3 kg/m~3 cutoff grade. However, a mineable reserve has not yet been completely determined.Mining method is by regular open-cut style. Excavation and haulage are undertaken by a simple fleet of backhoes and trucks. Run-of-mine (ROM) ore are transported to on-site processing plants. Overburden and oversized waste from processing plants are conveyed to dumping area.Processing steps to produce tin concentrate can be divided into 2 operations, namely the crude (primary) concentration operation and the tin shed operation. The primary concentration operation commences with dumping ROM material into the hopper, where it is loosened and washed by high pressure water jet from 2 nozzles (so-called the monitors). A 4-inch bar grizzly is used to remove oversized stones and two trommels (2.5 and 3/4 inches) are used to further remove oversized gravels. Then the material is sent to a series of palongs (sluicing boxes). Concentrates from riffles of palongs are passed to primary and secondary jigs and finally to a series of shaking tables. At this point the concentrate is around 30-40%Sn. In the tin shed operation, crude concentrates from the previous operation are treated by simple but laborious processes, performed manually. A "Willoughby Washer" is used as the hydraulic classifier, in conjunction with a short sluice known as the "Lanchute". After that the concentrates are passed through a drying process and finally with magnetic separation. The product is a marketable grade at more than 72%Sn. Currently the efficiency and recovery ratio are uncertain but are unlikely to be high. Monazite is one of major by-products of the mine. However, the mine has not yet established the exact strategy for the monazite. They are currently secured and stored on site in a secure place. From analysis of a few samples, the monazite contains some REE (mainly Ce) but the contents of Th and U are quite low. low and intermittent flow rates for 6 months are required in order to obtain sufficient data for further process commercialization.