Our various subsidiaries control 100% of the Greens Creek mine. Greens Creek produced a total of 7.5 million ounces of silver and 67,278 ounces of by-product gold in 2009, at the low average total cash cost of $0.35 per ounce of silver. The average ore grade was 13.01 ounces of silver per ton.
Information with respect to production, average costs per ounce of silver produced and proven and probable ore reserves is set forth below, and represents our 100% ownership of Greens Creek after April 16, 2008, and our previous 29.7% ownership prior to that date.
Year Ended December 31, | Production | 2009 | 2008 | 2007 | |
| Ore milled (tons) | 790,871 | 598,931 | 217,691 | |
| Silver (ounces) | 7,459,170 | 5,829,253 | 2,570,701 | |
| Gold (ounces) | 67,278 | 54,650 | 20,218 | |
| Zinc (tons) | 70,379 | 52,055 | 18,612 | |
| Lead (tons) | 22,254 | 16,630 | 6,252 | |
| Average Cost per Ounce of Silver Produced (1) |
2009 | 2008 | 2007 | |
| Total cash costs | 0.35 | 3.29 | $(5.27) | |
| Total production costs | 7.65 | 8.52 | $(1.93) | |
| Proven & Probable Ore Reserves (2,3,4,5,6,7) |
2009 | 2008 | 2007 | |
| Total tons | 8,314,700 | 8,064,700 | 2,513,700 | |
| Silver (ounces per ton) | 12.1 | 13.7 | 13.7 | |
| Gold (ounces per ton) | 0.10 | 0.11 | 0.11 | |
| Zinc (percent) | 10.3 | 10.5 | 10.2 | |
| Lead (percent) | 3.6 | 3.8 | 3.8 | |
| Contained silver (ounces) | 100,973,300 | 110,583,200 | 34,497,800 | |
| Contained gold | 847,400 | 870,100 | 270,000 | |
| Contained zinc (tons) | 852,900 | 850,700 | 255,900 | |
| Contained lead (tons) | 303,300 | 308,700 | 95,300 |
(1) Includes by-product credits from gold, lead and zinc production. Cash costs per ounce of silver represent measurements that are not in accordance with GAAP that management uses to monitor and evaluate the performance of our mining operations. We believe cash costs per ounce of silver provide an indicator of profitability and efficiency at each location and on a consolidated basis, as well as providing a meaningful basis to compare our results to those of other mining companies and other mining operating properties.
(2) Estimates of proven and probable ore reserves for the Greens Creek unit as of December 2009, 2008 and 2007 are derived from successive generations of reserve and feasibility analyses for different areas of the mine each using a separate assessment of metals prices. The weighted average prices used for reserve estimates in 2007, prior to our acquisition of the remaining 70.3% interest in Greens Creek, were determined by the geology and engineering staff of the Kennecott Greens Creek Mining Company, then an indirect subsidiary of Rio Tinto, plc, with our technical support. The 2007 prices differ from the prices used by us, for example, in making such calculations for our Lucky Friday unit for that year. We reviewed the geologic interpretation and reserve methodology, but the reserve compilation for 2007 for Greens Creek was not independently confirmed by us in its entirety. The average prices used for the Greens Creek unit were:
| 2009 | 2008 | 2007 | |
| Silver | $13.75 | $12.25 | $8.00 |
| Gold | $775 | $650 | $529 |
| Lead | $0.70 | $0.80 | $0.27 |
| Zinc | $0.70 | $0.80 | $0.58 |
(3) Ore reserves represent in-place material, diluted and adjusted for expected mining recovery. Mill recoveries of ore reserve grades differ by ore zones and are expected to average 74% for silver, 68% for gold, 77% for zinc and 73% for lead.
(4) The changes in reserves in 2008 versus 2007 are due to our acquisition of the remaining 70.3% of Greens Creek in April 2008, along with the addition of new drill data and increases in forecasted precious metals prices, partially offset by depletion due to production.
(5) We only report probable reserves at the Greens Creek unit, which are based on average drill spacing of 50 to 100 feet. Proven reserves typically require that mining samples are partly the basis of the ore grade estimates used, while probable reserve grade estimates can be based entirely on drilling results. Cutoff grade assumptions vary by orebody and are developed based on reserve prices, anticipated mill recoveries and smelter payables and cash operating costs. Cutoff grades range from $97 per ton net smelter return to $107 per ton net smelter return.
(6) Reflects our 29.7% ownership interest until April 16, 2008, and our 100% ownership thereafter.