Inventory Accounting Policy
Inventories
The largest components of inventories include finished goods (primarily concentrates and cathodes) at mining operations, concentrates and work-in-process at Atlantic Copper's smelting and refining operations, and materials and supplies inventories. Inventories of materials and supplies, as well as salable products, are stated at the lower of weighted-average cost or market. Costs of finished goods and work-in-process (i.e., not materials and supplies) inventories include labor and benefits, supplies, energy, depreciation, depletion, amortization, site overhead costs and other necessary costs associated with the extraction and processing of ore, including, depending on the process, mining, haulage, milling, concentrating, smelting, leaching, solution extraction, refining, roasting and chemical processing. Corporate general and administrative costs are not included in inventory costs.
Work-in-Process. In-process inventories represent materials that are currently in the process of being converted to a salable product. Conversion processes for mining operations vary depending on the nature of the copper ore and the specific mining operation. For sulfide ores, processing includes milling and concentrating and results in the production of copper and molybdenum concentrates or, alternatively, copper cathode by concentrate leaching. For oxide ores and certain secondary sulfide ores, processing includes leaching of stockpiles, solution extraction and electrowinning (SX/EW) and results in the production of copper cathodes. In-process material is measured based on assays of the material included in these processes and projected recoveries. In-process inventories are valued based on the costs incurred to various points in the process, including depreciation relating to associated process facilities. For Atlantic Copper, in-process inventories represent copper concentrates at various stages of conversion into anodes and cathodes. Atlantic Copper's in-process inventories are valued at the weighted-average cost of the material fed to the smelting and refining process plus in-process conversion costs.
Finished Goods. Finished goods include salable products (e.g., copper and molybdenum concentrates, copper anodes, copper cathodes, copper rod, copper wire, molybdenum oxide, high-purity molybdenum chemicals and other metallurgical products). Finished goods are valued based on the weighted-average cost of source material plus applicable conversion costs relating to associated process facilities.
Mill and Leach Stockpiles
Mill and leach stockpiles are stated at the lower of weighted-average cost or market. Both mill and leach stockpiles generally contain lower grade ores that have been extracted from the ore body and are available for copper recovery. For mill stockpiles, recovery is through milling, concentrating, smelting and refining or, alternatively, by concentrate leaching. For leach stockpiles, recovery is through exposure to acidic solutions that dissolve contained copper and deliver it in solution to extraction processing facilities. The recorded cost of mill and leach stockpiles includes mining and haulage costs incurred to deliver ore to stockpiles, depreciation, depletion, amortization and site overhead costs.
Because it is generally impracticable to determine copper contained in mill and leach stockpiles by physical count, reasonable estimation methods are employed. The quantity of material delivered to mill and leach stockpiles is based on surveyed volumes of mined material and daily production records. Sampling and assaying of blasthole cuttings determine the estimated copper grade of the material delivered to mill and leach stockpiles.
Expected copper recovery rates for mill stockpiles are determined by metallurgical testing. The recoverable copper in mill stockpiles, once entered into the production process, can be produced into copper concentrate almost immediately.
Expected copper recovery rates for leach stockpiles are determined using small-scale laboratory tests, small- to large-scale column testing (which simulates the production-scale process), historical trends and other factors, including mineralogy of the ore and rock type. Ultimate recovery of copper contained in leach stockpiles can vary significantly from a low percentage to more than 90 percent depending on several variables, including type of copper recovery, mineralogy and particle size of the rock. For newly placed material on active stockpiles, as much as 70 percent of the copper ultimately recoverable may be extracted during the first year, and the remaining copper may be recovered over many years.
Processes and recovery rates are monitored regularly, and recovery rate estimates are adjusted periodically as additional information becomes available and as related technology changes.
Source: Freeport-McMoRan Copper & Gold Inc., Annual Report
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