Inventories - Additional Information (Detail) - USD ($)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Inventory [Line Items]
Cost of materials and supplies consumed	$ 87,269,000	$ 120,422,000
Inventory write-down	1,465,000	444,000
Zinc [member]
Inventory [Line Items]
Inventory write-down	269,000	444,000
Pyrite [Member]
Inventory [Line Items]
Inventory write-down	$ 1,196,000	$ 0

The amount of expense recognised related to the write-down of inventories to net realisable value. [Refer: Inventories]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 2
-IssueDate 2018-01-01
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-URIDate 2018-03-16

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2018-01-01
-Paragraph 98
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_98_a&doctype=Standard
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