forming in the winter, the installation of a metal brattice, repair of shaft steel, and installation of a new power cable, all of which should improve the  shaft’s functionality and possibly improve the shaft’s hoisting capacity. Production was temporarily suspended during all of 2012 as the Silver Shaft  rehabilitation work was performed. During the suspension of production, the smelter contracts related to treatment of Lucky Friday concentrates were  suspended based on  force majeure . The shaft restoration project and other related work has been completed, with limited production at the Lucky  Friday recommencing in early 2013. We anticipate a ramp-up in mine output during the first half of the year as additional production areas come on  line, with a return to full production levels expected in mid-2013. However, the timing of the return to full production at the Lucky Friday mine may  ultimately vary from our current estimates. Once the Silver Shaft rehabilitation work was completed down to the 4900 level, we commenced  construction of a haulage way bypass around an area impacted by a rock burst in December 2011, and completed the bypass in early 2013.  Completion of work on the Silver Shaft to the 4900 level also enabled planning and other preliminary work to resume on the #4 Shaft project (discussed  below), and we resumed sinking of #4 Shaft in early 2013 upon completion of the Silver Shaft work. Care and maintenance costs incurred at the Lucky  Friday during the suspension of production totaled $25.3 million, including $6.3 million in depreciation, depletion, and amortization, in 2012. These  costs are included in a separate line item under  Other operating expenses  on the  Consolidated Statement of Operations and Comprehensive  Income. Depreciation, depletion, and amortization expense at Lucky Friday of $6.3 million for 2012 was included in  Lucky Friday suspension-related costs  under  Other operating expenses  on the  Consolidated Statement of Operations and Comprehensive Income . Depreciation, depletion, and  amortization expense for 2011 was 27% lower than in 2010 due to reduced units-of-production depreciation. The majority of the decrease was  incidental to an extension of expected mine life at Lucky Friday, resulting in the book value of units-of-production assets being depreciated over a  longer duration. The extension of the expected mine life is primarily due to the positive economics of the #4 Shaft project which, when completed, will  provide deeper access beyond the current workings (see below for further discussion of the #4 Shaft project). In addition, production was lower in 2011  compared the previous year, primarily due to down-time related to the accidents discussed below. Mining and milling costs per ton increased in 2011 by 12% and 15%, respectively, compared to 2010 primarily due to lower production and higher  costs of fuel, consumable underground materials, reagents, and maintenance supplies.  The chart below illustrates the factors contributing to the variances in total cash costs per silver ounce for 2011 and 2010: Mining and milling costs per ounce increased in 2011 compared to 2010 due to the higher cost of consumables and supplies. The higher other cash  costs per ounce in 2011 are mainly due to increased profit sharing, as a result of higher silver prices and profits. Treatment costs increased in 2011 due  to higher lead prices, as treatment costs include a price participation component that fluctuates with changes in base metal prices. The increase in by- product credits in 2011 is also attributable to the higher lead prices, partially offset by lower lead and zinc production in 2011 compared to 2010. The difference between what we report as “production” and “payable metal quantities sold” is due to the difference between the quantities of  metals contained in the concentrates we produce versus the portion of those metals actually paid for by our smelter customers according to the terms  of the smelter contracts (not all of the metals contained in our concentrate shipments are physically recovered through the smelting process). The  decrease in payable quantities sold in 2011 compared to 2010 is attributable to a decrease in production due mainly to various down-time periods  related to the accidents discussed below. While revenue from lead and zinc is significant at the Lucky Friday, we believe that identification of silver as the primary product, with lead and zinc  as by-products, is appropriate because: We periodically review our revenues to ensure that reporting of primary products and by-products is appropriate. Because we consider lead and  zinc to be by-products of our silver production, the values of these metals offset operating costs within our cost per ounce calculations. y silver has historically accounted for a higher proportion of revenue than any other metal and is expected to do so in the future; y the Lucky Friday unit is situated in a mining district long associated with silver production; and y the Lucky Friday unit generally utilizes selective mining methods to target silver production. 26 [ HL:10-K ]  Years Ended December 31 ($ per ounce produced) mining and milling 2011 2010 $ 7.78 $ 7.21 other cash costs 2011 2010 $ 7.57 $ 6.17 treatment costs 2011 2010 $ 6.66 $ 5.46 concentrate freight 2011 2010 $ 0.68 $ 0.64 by-product credit 2011 2010 ($ 16.22) ($ 15.72) Year 2011 2010 $ 6.47 $ 3.76 Cash cost per ounce