This technical report presents a preliminary economic assessment of the Song Toh and Boh Yai properties in Kanchanaburi Province, Thailand, as of March 31, 2013.
Report context
This technical report, effective March 31, 2013, describes the Song Toh and Boh Yai properties located in the Meklong Highlands region of Kanchanaburi Province, Thailand, approximately 300 km northwest of Bangkok. The report is a preliminary economic assessment for Southeast Asia Mining Corp. covering mineral processing and metallurgical activities at the two former lead-zinc mines. The Song Toh mine operated from 1978 to 2002, while the Boh Yai mine operated from 1988 to 2002. The report presents a proposed design for renewed operations based on historical mining and processing data, with supporting metallurgical testwork.
Processing route
Historical flotation plant
Between 1978 and 2002, a total of 5,237,800 tonnes of ore was produced and milled at the flotation plant located near Song Toh. This produced 648,760 tonnes of lead and zinc concentrates. In 2008, a further 60,000 tonnes of ore from a stockpile was produced and milled. The plant is a standard Pb-Zn flotation circuit that can be operated at between 25 and 50 tonnes per hour depending on the type of feed. Both sulfide feed from underground mining and oxide feed from surface mining have been treated at the plant. The milling plant and equipment are reported in fair to good condition with much service life remaining. Some repairs and upgrades are required, and additional equipment for spares or expansion of the plant is available locally.
Tailings management area
The tailings from the plant are stored locally in a tailing management area consisting of three discrete cells. One cell had been used in the past to store thickened tailings produced by a classifier associated with the mill, which remain in storage for possible reprocessing. The other two cells, formed by a separator dyke, represent the main tailing management area. The dam forming the tailing management area is constructed of spigotted tailing and was built in three lifts using the upstream method of construction. The structure is approximately 10 to 25 m high with a 5 m top width on the upper bench. No slumping or excessive lateral or longitudinal cracking was observed during inspection. Slope angles were considered to be at the upper range for dams of this height. The tailing management area had been upgraded just prior to cessation of operations, with further upgrading required to create capacity for the remaining resource.
Proposed processing design
The report presents a proposed design for the flotation circuit based on the historical plant configuration and operating parameters. The proposed design envisions processing ore from both Song Toh and Boh Yai deposits through the existing flotation plant. The circuit is designed for standard Pb-Zn sulfide flotation, with provision for treating oxide ore. The plant throughput is designed to operate within the range of 25 to 50 tonnes per hour, consistent with historical operating rates.
Historical ore transportation
Historically, ore from the Song Toh underground mine was hauled up the ramp to surface and to the mill by 10-wheel, 15-tonne capacity trucks. The processing plant is located near Song Toh, and ore from Boh Yai was transported to the plant via a 14 km gravel road linking Song Toh directly with Boh Yai.
Historical mine water management
Water ingress was a significant problem at the Song Toh underground operations due to the presence of karstic limestone and associated sinkholes and caves. Water inflows sometimes exceeded 40 m³/min during the rainy season. When pumping costs at Song Toh North became excessive, a drainage tunnel 1,700 m long was developed at 545 m elevation, with outflow at Huai Chanee Creek. The drainage tunnel was subsequently extended for 1,650 m to drain Song Toh South at an elevation of 555 m. At Boh Yai, a main haulage drift was completed for 2,200 m and serves as a dewatering drift to drain a high flow rate caused by karst features, which may exceed 25 m³ per minute during the rainy season.
Historical mine backfill practices
At Song Toh, steeply dipping parts of the orebody were exploited by overhead open stoping, with backfill using normal waste subject to mining loss of 5-12%. In high-grade areas, concrete backfill was used to allow extraction of pillars and reduce mining loss to less than 5%. Shallow-dipping parts of the orebody were exploited by room and pillar mining, subject to mining losses of up to 20%. At Boh Yai, room and pillar method was used with mining loss of 15-20%. Other methods were precluded by the difficulty of obtaining economical backfill above the main haulage drift and low metal prices which rendered replacement of ore pillars by concrete uneconomic.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Flotation plant throughput | 25-50 t/h | Design range (historical operating range) |
| Historical ore milled (1978-2002) | 5,237,800 t | Historical operating data |
| Historical concentrate produced (1978-2002) | 648,760 t | Historical operating data |
| 2008 stockpile ore milled | 60,000 t | Historical operating data |
| Tailings dam height | 10-25 m | Design specification |
| Tailings dam top width | 5 m | Design specification |
| Tailing management area cells | 3 | Design specification |
| Historical water inflow, Song Toh | >40 m³/min (rainy season) | Historical operating data |
| Historical water inflow, Boh Yai | >25 m³/min (rainy season) | Historical operating data |
| Song Toh drainage tunnel length | 1,700 m (initial), 1,650 m (extension) | Historical operating data |
| Song Toh drainage tunnel elevation | 545 m (initial), 555 m (extension) | Historical operating data |
| Boh Yai main haulage/dewatering drift length | 2,200 m | Historical operating data |
| Boh Yai main haulage/dewatering drift elevation | 555 m level to 565 m level | Historical operating data |
Technical qualifications
The processing information in this report is based on a preliminary economic assessment. The report states that some repairs and upgrades are required to the milling plant, and additional equipment for spares or expansion is available locally. The report notes that the tailing management area had been upgraded just prior to cessation of operations, with further upgrading required to create capacity for the remaining resource. No new metallurgical testwork was conducted for this report; the processing data is derived from historical operating records and existing plant design parameters.
Source: Technical Report and Preliminary Economic Assessment of the Song Toh – Boh Yai Properties, Kemco Project, Thong Phaphum District, Kanchanaburi Province, Thailand, Report No. 968, effective March 31, 2013.
