INTANGIBLE ASSETS: (Tables)

12 Months Ended

Dec. 31, 2023

INTANGIBLE ASSETS:

Schedule of major classes of intangible assets and goodwill

	At December 31,
(in millions)	2023		2022
Mining concessions	$	121.2	$	121.2
Mine engineering and development studies		19.8		19.8
Software		74.3		70.3
		215.3		211.3
Accumulated amortization:
Mining concessions		(44.2)		(42.2)
Mine engineering and development studies		(19.8)		(19.2)
Software		(63.0)		(57.1)
		(127.0)		(118.5)
Goodwill		41.9		41.9
Intangible assets, net	$	130.2	$	134.7

Schedule of estimated amortization of intangible assets for future periods

Estimated amortization expense (in millions):
2024	$	6.3
2025		6.0
2026		2.1
2027		2.1
2028		2.0
Total 2024 - 2028	$	18.5
Average annual	$	3.7