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BENEFIT PLANS: | 6 Months Ended
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Jun. 30, 2026
BENEFIT PLANS: |
BENEFIT PLANS: | ​ NOTE 9 — BENEFIT PLANS: ​ Post retirement defined benefit plans: ​ The Company’s Mexican subsidiaries have a defined contribution pension plan for salaried employees and a non-contributory defined benefit pension plan for union employees. In addition, the Company had a noncontributory defined benefit pension plan covering former salaried employees in the United States and certain former expatriate employees in Peru (the “Expatriate Plan”). On July 24, 2025, the Board of Directors of the Company authorized the termination of the Expatriate Plan. This termination became effective December 1, 2025 and had no material impact on the Company’s financial statements. The Expatriate Plan’s benefit obligation was settled by the purchase of annuity contracts to transfer the plan’s remaining obligations to third parties. The termination process was completed on April 30, 2026. ​ The components of net periodic benefit costs for the six-month periods ended June 30, 2026 and 2025 are as follows (in millions): ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Six months ended
​ | ​ | June 30,
(in millions) | ​ ​ ​ | 2026 | ​ ​ ​ | 2025
Service cost | ​ | $ | 1.6 | ​ | $ | 1.2
Interest cost | ​ |  | 2.0 | ​ |  | 1.9
Expected return on plan assets | ​ |  | (4.7) | ​ |  | (3.6)
Amortization of prior service cost / (credit) | ​ |  | 0.1 | ​ |  | 0.1
Amortization of net loss/(gain) | ​ |  | (0.6) | ​ |  | 0.1
Net periodic (benefit) cost | ​ | $ | (1.6) | ​ | $ | (0.3)
​ Post-retirement health care plans: ​ Starting in 2011, the Mexican Institute of Social Security began providing health care services to retired workers of the Buenavista unit and their families. These services are free of charge to the retired workers, and their costs are covered by the Company. ​ The components of net periodic benefit cost for the six-month periods ended June 30, 2026 and 2025 are as follows (in millions): ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Six months ended June 30,
(in millions) | ​ ​ ​ | 2026 | ​ ​ ​ | 2025
Interest cost | ​ | $ | 1.2 | ​ | $ | 1.0
Amortization of net loss (gain) | ​ |  | — | ​ |  | —
Net periodic cost | ​ | $ | 1.2 | ​ | $ | 1.0
​

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