Classification of Ni Levels for Determination Cut-Off Grade in Region X

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INTRODUCTION
A mineral resource is a concentration or occurrence of material that has economic value on or above the earth's crust, with a certain shape, quality, and quantity that has reasonable prospects for eventually being economically extracted (Sukandarrumidi, 2007). Nickel laterite is one type of natural resource that cannot be renewed, this is because the formation of nickel laterite requires a process that takes millions of years (Thamsi, Jafar, and Fauzie 2021a;Yogi Pranata et al. 2017).
Some of the factors that form nickel include rock of origin, climate, chemical reagents and vegetation, structure, topography, and time (Waheed, 2002;Hardyanto 2016;Hasria et al. 2021;Yogi Pranata et al. 2017). The need for high-grade mills causes ore, ore itself is a valuable mineral that is sought and then extracted in mining activities with the hope (although not always achieved) to gain benefits for miners and for the community (Taylor, 1986). Low-grade ore will lose the selling price and will be categorized as waste because it cannot be processed at the factory (Habibie et al., 2019). This condition certainly requires proper handling so that low-grade ore is not wasted and the volume of reserves increases (Azizi et al., 2019;Ilyas et al., 2022;Sufriadin et al., 2012;Thamsi, 2017).
One of the unresolved problems in Region X is the determination of the cut-off grade. Region X itself has low levels or can be said to be incompatible with the products targeted by the company. The product targeted by the company is an ore which has a Ni content of 1.8%. Cut off grade or limit grade where the grade below has metal or mineral content in rock that does not meet economic requirements (Heriyawan et al, 2005(Anshariah, 2016Syah et al., 2018;Thamsi et al., 2021).

RESULTS AND DISCUSSION Distribution of Ni in Region X
The nickel distribution picture shows the distribution of nickel with levels represented by several colors, including blue, light blue, green, light green, yellow and red. The red color in the figure represents nickel with the highest grade of 2.5 -3%, with the least volume in Region X. In addition to red, nickel with a high grade is also represented by yellow with a content of 2 -2.5%, total volume nickel represented by red and yellow is 15,650 Bcm. Other colors shown in the picture are green and light green. The green color in the picture above represents nickel with levels of 1 -1.5%, while the light green color represents nickel with levels of 1.5 -2%; these two colors dominate Region X because Region X is the area with the highest nickel content is 1-2 % total volume is 140,100 Bcm ( Figure 1). Nickel with the lowest levels in Region X is shown in blue and light blue, i.e., 0-1%. Nickel with levels below 1% is considered waste or material that is considered waste and is not recommended for mining.

Mining Stage
The mining sequence carried out in Region X is carried out in stages, starting from the part with less waste material and more material containing nickel with levels above 1%. The mining sequence in Region X is divided into 3 stages. gradually, nickel grades above 1% are 89,936 tons, 442,359 tons, and 100,558 tons. If seen briefly in Figure 2, the ore with high levels is not very visible on the surface; this is because, in the second area, there is only a little more with high levels, which can be seen clearly in table 2 below.
From the results of the classification of levels of Ni at the last stage, nickel with the highest grade that can be obtained is nickel with a grade of 2.6 -2.8% but with a very small tonnage of 979 tons with an average grade of 2.7% (Figure 3 and Table 3).
After calculating the formula for determining the total volume, average grade, and tonnage in each classification, the results obtained from these calculations can be seen in Table 4 No. Ni

2.7
Blending Stage Simulation Blending is mixing materials of different quality and quantities to obtain an appropriate mixture. In the blending process, it must meet the specific ore needs of the processing plant (Musnajam, 2012). In the blending process, it must meet the specific ore needs of the processing plant, where the factory requires ore with a Ni content of 1.8%.
It can be done with the formula Average content to calculate the average level of blending ore results on the stockpile. Formula: Average Ni Content = (V1xNi) + ⋯ + (Vn x Ni n) V total Table 5. Simulation of blending stages

CONCLUSION
From the results of the discussion described previously, it can be concluded that the cut-off grade used in area X is 1.6, with a total tonnage of 71,086 tons by blending ore to optimize nickel with low grades.
From the above calculation results, the blending carried out in the first stage by mixing all ores with a high content of 1.8% and above resulted in a relatively high average content of 2.07%. This means that the lower grade can still be mined, so it is necessary to re-mix it with nickel with a lower grade classification. The results of the calculation of the average grade are possible to be used as a benchmark for determining the cut-off grade, namely the Ni classification, which has a grade above 1.6% with an average grade of 1.9%, and the total tonnage of ore that can be mined is 71.086 tons. This is proven in the calculation of the third stage of the simulation.