INTANGIBLE ASSETS: (Tables)

12 Months Ended

Dec. 31, 2020

INTANGIBLE ASSETS:

Schedule of major classes of intangible assets and goodwill

	At December 31,
(in millions)	2020		2019
Mining concessions	$	121.2	$	121.2
Mine engineering and development studies		19.8		19.8
Software		60.6		55.9
		201.6		196.9
Accumulated amortization:
Mining concessions		(38.6)		(38.0)
Mine engineering and development studies		(17.2)		(16.3)
Software		(44.7)		(36.1)
		(100.5)		(90.4)
Goodwill		41.9		41.9
Intangible assets, net	$	143.0	$	148.4

Schedule of estimated amortization of intangible assets for future periods

Estimated amortization expense (in millions):
2021	$	7.7
2022		5.2
2023		5.2
2024		4.3
2025		3.0
Total 2021 - 2025	$	25.4
Average annual	$	5.1