SEGMENT AND RELATED INFORMATION: (Details) $ in Millions	3 Months Ended
Mar. 31, 2020 USD ($) segment	Mar. 31, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2019 USD ($)
Financial information related to segments
Number of reportable segments \| segment	3
Financial information relating to segments
Net sales	$ 1,719.7	$ 1,753.4	$ 1,753.4
Cost of sales (exclusive of depreciation, amortization and depletion)	955.8	844.1
Selling, general and administrative	29.1	28.5
Depreciation, amortization and depletion	192.9	181.6
Exploration	8.6	5.5
Operating income	533.3	693.7
Interest, net	(89.0)	(74.1)
Other income (expense)	(7.4)	5.4
Income taxes	(221.7)	(237.9)
Equity earnings of affiliate	1.0	2.1
Non-controlling interest	(1.4)	(1.0)
Net income attributable to SCC	214.8	388.2
Capital investment	101.0	173.1
Property and mine development, net	9,288.7	9,383.6		$ 9,371.0
Total assets	16,212.1	15,542.6		$ 16,407.4
Intersegment sales
Financial information relating to segments
Net sales	(26.8)	(19.9)
Corporate, other and eliminations
Financial information relating to segments
Net sales	(26.8)		(19.9)
Cost of sales (exclusive of depreciation, amortization and depletion)	(32.5)	(23.5)
Selling, general and administrative	0.9	0.8
Depreciation, amortization and depletion	9.6	8.8
Exploration	3.4	0.2
Operating income	(8.2)	(6.2)
Capital investment	2.3	1.1
Property and mine development, net	529.8	343.7
Total assets	3,651.5	1,588.8
Reportable subsegments
Financial information relating to segments
Net sales	1,719.7	1,753.4
Mexican Open-pit \| Operating segment
Financial information relating to segments
Net sales	953.7		1,072.1
Cost of sales (exclusive of depreciation, amortization and depletion)	465.1	419.6
Selling, general and administrative	16.7	16.3
Depreciation, amortization and depletion	91.4	85.0
Exploration	0.7	0.4
Operating income	379.8	550.8
Capital investment	38.2	58.6
Property and mine development, net	4,420.7	4,780.6
Total assets	7,057.2	8,375.0
Mexican Open-pit \| Reportable subsegments \| Operating segment
Financial information relating to segments
Net sales	953.7	1,072.1
Mexican IMMSA Unit \| Operating segment
Financial information relating to segments
Net sales	134.5		121.1
Cost of sales (exclusive of depreciation, amortization and depletion)	112.2	100.0
Selling, general and administrative	2.4	1.8
Depreciation, amortization and depletion	10.6	12.9
Exploration	2.9	2.0
Operating income	6.4	4.4
Capital investment	25.3	25.0
Property and mine development, net	505.7	460.9
Total assets	815.9	942.2
Mexican IMMSA Unit \| Intersegment sales
Financial information relating to segments
Net sales	26.8	19.9
Mexican IMMSA Unit \| Reportable subsegments \| Operating segment
Financial information relating to segments
Net sales	107.7	101.2
Peruvian Operations \| Operating segment
Financial information relating to segments
Net sales	658.3		$ 580.1
Cost of sales (exclusive of depreciation, amortization and depletion)	411.0	348.0
Selling, general and administrative	9.1	9.6
Depreciation, amortization and depletion	81.3	74.9
Exploration	1.6	2.9
Operating income	155.3	144.7
Capital investment	35.2	88.4
Property and mine development, net	3,832.5	3,798.4
Total assets	4,687.5	4,636.6
Peruvian Operations \| Reportable subsegments \| Operating segment
Financial information relating to segments
Net sales	$ 658.3	$ 580.1

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Exploration expenses (including prospecting) related to oil and gas producing entities and would be included in operating expenses of that entity. Costs incurred in identifying areas that may warrant examination and in examining specific areas that are considered to have prospects of containing oil and gas reserves, including costs of drilling exploratory wells and exploratory-type stratigraphic test wells. Exploration costs may be incurred both before acquiring the related property (sometimes referred to in part as prospecting costs) and after acquiring the property. Principal types of exploration costs, which include depreciation and applicable operating costs of support equipment and facilities and other costs of exploration activities, are: (i) Costs of topographical, geographical and geophysical studies, rights of access to properties to conduct those studies, and salaries and other expenses of geologists, geophysical crews, and others conducting those studies. Collectively, these are sometimes referred to as geological and geophysical or "G&G" costs. (ii) Costs of carrying and retaining undeveloped properties, such as delay rentals, ad valorem taxes on properties, legal costs for title defense, and the maintenance of land and lease records. (iii) Dry hole contributions and bottom hole contributions. (iv) Costs of drilling and equipping exploratory wells. (v) Costs of drilling exploratory-type stratigraphic test wells.

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