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Independent team, PTNNT have similar concentrate assay results PDF Cetak E-mail
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Rabu, 16 Februari 2011 14:59
West Sumbawa, An assay of minerals contained in PT Newmont Nusa Tenggara (PTNNT)’s concentrate by an Independent Team of the Environmental Impacts Monitoring and PTNNT’s Concentrate Products Evaluation in 2003 showed similar results to the ones the company reported to the government.

 The report of the Independent Team established under West Nusa Tenggara Governor Decree No. 180 of 2003 mentions that copper (Cu) is the most dominant composition in the concentrate with concentration of 29.51 – 36.38%, followed by silver (Ag) and gold (Au) with concentration of 73.8 – 82.0 ppm and 23.22 – 29.39 ppm respectively.

“This data shows that PTNNT conducts mining of the copper ore as the main mineral,  while gold and silver are just associated minerals,” states the report of Independent Team led by Dr. H. Zainal Asikin, S.H., S.U.

For the concentrate assay, the independent team collected samples from 20,800 tons of concentrate at the 34th shipment that would be exported by MV CS Valiant to Japan. Analysis method used international-standard Umpire level (with highest accuracy in analyzing concentrate grade). The sample was then analyzed at Sucofindo laboratory in Surabaya.  

 “The 2003 study by the Independent Team was evidence that we are committed to running our operation transparently. We always welcome each government office who is interested in learning about the assay process of the concentrates,” said Arif Perdanakusumah, PTNNT’s Senior Manager for External Relations.

 PTNNT is a contractor of the Government of Indonesia in accordance with its Contract of Work signed in 1986. The company has run a copper and gold mining operation at Batu Hijau, West Sumbawa since 2000. The company produces concentrates and sells them to domestic and overseas smelters. The company complies with all of government’s regulation and international business practices in selling its concentrates. In 2010, the company paid all its financial obligations totaling Rp.5.76 trillion to the state.  

The Batu Hijau porphyry copper deposit contains very little gold and silver deposits. The valuable metals can indirectly be recovered because they mix with other non-valuable minerals. The porphyry deposit is identified only containing low grade. At Batu Hijau, each tonne of the processed    ore only produces 4.87 kilograms. While the average gold recovered is much fewer, namely 0.37 grams a tonne of processed ore. This indicates that to produce few salable metal requires hard work. Mining at Batu Hijau begins with drilling and blasting to allow ore recovery. The ore is then transported to the concentrator, while lower grade rocks are transported to stockpile area, pending the next process in the future.      

At the concentrator, the valuable minerals are separated from the rocks through grinding and flotation process. Flotation process does not use chemical substance excessively so that the process is always safe and helps minimize the environmental impacts.  With physics process, the valuable minerals are separated from the rocks using bubbles and reagents in little quantity. From flotation cells, the concentrate is transported to the counter current decantation (CCD) tank. In this tank, seawater is disposed of and the concentrate is thickened by flowing freshwater in opposite direction. The freshwater substitutes the seawater and the concentrate sinks and settles at the bottom of the tank. Upon the filtration process the concentrate will be in the form of fine powder and stored at the concentrate silo before the shipment.        

Eventually, the concentrate is shipped to a domestic smelter, i.e. PT Smelting in Gresik, East Java, and overseas smelters, i.e.  Japan, South Korea, India, Europe, where the concentrate is separated to get precious metals, i.e. copper, gold, and silver.**
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