07 July, 2007 07:35
As the mine life of its Gold and Silver Project marks the end of its third year, TVI Resource Development Philippines, Inc. (TVIRD) is looking to begin the second phase of its operations in Canatuan, the Copper Zinc Project, also known as the Sulphide Project.
The Company is in the process of building a tailings storage dam and impoundment, which is a major component of the Sulphide Project. The Sulphide ore will be extracted from the same open pit from which the Company is currently extracting gossan ore to get gold and silver.
After extraction, however, the workflow is completely different. For this project, TVIRD will need to build a new mill plant to process the ore. The mill process residual product, known as tailings, will need to be sent to a new dam made specifically to hold the Sulphide tailings and to prevent the discharge of tailings into neighboring bodies of water.
While the design and construction of this new dam will be similar to the previously constructed Gossan Tailings Dam, the operational aspects will be different. In the Gossan Dam, the tailings are pumped into the impoundment as a slurry where they remain. Water, which is part of the slurry, eventually evaporates and the tailings surface dries up over time. In time, the exposed tailings surface can be rehabilitated as grasslands, forest areas or turned into a cash crop plantation style agricultural area.
The primary operational difference between the Gossan tailings and the Sulphide tailings disposal is that the Sulphide tailings should remain in a non oxidized state to avoid generation of acid mine drainage. Therefore, unlike the Gossan tailings, which can be left exposed and used for agricultural or forestry purposes, the Sulphide tailings must be protected from contact with air thereby preventing initiation of the oxidation process. This is done by maintaining a constant water cover over the tailings and operating the impoundment as a continuous water impoundment.
To design this specialized dam, TVIRD contracted Smith-Williams Consultants, a firm based in Denver, Colorado. Smith-Williams visited the Canatuan site in 2006 to find a possible location of the dam and review the strength of the foundation soil in the area. The design phase then took around two to three months.
Engineer Jeff Gibby, an employee of Smith-Williams, has been in Canatuan since January 2007. He has been closely working with Jay Nelson, TVIRD Vice President for Environment and Civil Works, in overseeing the construction of the dam and in ensuring that the work being done is consistent with the design and that the quality is up to industry standards. Gibby has also made minor adjustments to the initial design plan as the construction progresses and new in the field information becomes available.
According to Gibby, the new dam is similar to those he has worked on before in other parts of the world, and the only differences are in the way the dam will make use of the contours of the site topography.
The dam, which will need a constant supply of fresh water, is located near the mouth of the Canatuan River. The river water impounded behind the dam will provide a minimum three- meter deep water barrier between the Sulphide tailings and the air in the atmosphere.
The water will be maintained at this elevation by a high level spillway. Fresh water discharged from the spillway will continue down the Canatuan River and eventually join with other rivers before emptying into the Philippine Sea.
Once completed, the initial construction phase of the dam will have placed nearlyone million cubic meters of earth, sand and rock fill. At this stage, the dam will be approximately 61 meters high and will have the capacity to store approximately 3.2 million tons of tailings. When TVIRD chooses to expand its operations, the dam will be extended to a height of 78 meters, which will more than double its tailings storage capacity.
Gibby said that the only complications that he has faced during the construction phase have been the rainy weather and the rugged terrain. According to him, the dry-season was not very dry, and the rainy-season has been very rainy. Consequently, the work has slowed down, and for two months the workers have been pumping the rainwater out from the construction area.
Most of the workers hired for the construction of the dam are from local and surrounding areas, providing additional benefits for TVIRD’s affected communities. While proper training can be time consuming, and involves a continual process, TVIRD believes that the skills learned will serve to enhance the long-term and sustainable livelihood of many indigenous workers beyond the dam construction project. As the construction progresses to later phases, the workers will need to be trained for new activities. Training could range from a couple of hours for the easier activities, to a week for the more complicated tasks.
Gibby has targeted September 2007 as the end date of construction. But if the weather continues to be a problem, work may not end until early 2008. (Andrew Dominguez)
