MODEL GEOLOGI DAN DESAIN PIT TAMBANG ENDAPAN NIKEL LATERIT PADA DAERAH WATUDEMBA, KECAMATAN PALANGGA, KABUPATEN KONAWE SELATAN PROVINSI SULAWESI TENGGARA

The purpose of study is to design pit based on geological model as well as economic model in study area. The study is actually a combination of geological model associated with the geological conditions of nickel laterite formation and the economic model associated with the assessment of Break Even Cut-Off Grade (BECOG) and land acquisition costs per ton of nickel laterite production for obtaining the optimum reserves. The study area is located in Exploration IUP of PT. X, Watudemba Village, District of Palangga, Konawe Selatan Regency, Southeast Sulawesi Province. Geomorphologic units within study area are weak-undulated denudational hills and weak-undulated denudational plain. Geological model at study area is dominated by sedimentary rocks of reef limestone laid unconformably above ultramafic igneous rocks. Ultramafic igneous rocks age was Cretaceous while reef limestone in Miocene age. Petrographic analysis suggests that the ultramafic igneous rock is typical of Harzburgit. Surface data acquisition was performed on the all of the Exploration IUP PT. X with an area of 705 ha while the subsurface data is in block 1 with an area of 110 ha and then obtained the prospect area with an area of 30 Ha. The important factor to determine the design mine pit of nickel laterite is assessment of BECOG which is obtained from mining costs and land acquisition costs per ton of nickel laterite production. As results, a BECOG value at 1,86% Ni with the cut-off grade (COG) of 1,50% Ni has the reserves of 3.604.228,13 tons with a mine life of 2,7 years. For 2 % Ni of BECOG value with 1,70% Ni cut-off grade, the amount of the reserve is 2.565.215,63 tons with a mine life of 1,9 years. BECOG value of 2,2% Ni with 1,80% Ni cut-off grade has the reserve of 2.186.278,13 tons with a mine life of 1,6 years. BECOG value of 2,3% Ni with 1,90% Ni cut-off grade is assumed to get reserve of 1.411.265,63 tons with a mine life of 1 year