The Sonora Company mines precious metals at excavation sites throughout North and South America. Although sales of copper and gold have flattened during the year and gold sales are well below the prior year, the company remains profitable, largely because of efficient mining technologies and a major company-wide cost containment program. No new sites have been discovered in the past two years and all existing mines have been depleted by no less than 50 percent. Sonora's chief executive officer is strongly considering a discretionary write-down of selected mines, arguing that the assets' values are significantly impaired.

Required: 

Identify, and explain the motive for, the key questions an auditor must ask to judge whether management's discretionary write-down of impaired assets is appropriate.