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Summary of significant accounting policies - Narrative (Details) - Mobile Equipment, Tailings Dam and Equipment	12 Months Ended
	Dec. 31, 2018
Bottom of range
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives of property, plant and equipment	3 years
Top of range
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives of property, plant and equipment	6 years

X

- Definition

Useful Lives Or Depreciation Rates, Property, Plant And Equipment, Period

+ References

No definition available.

+ Details

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X

- Definition

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

+ References

No definition available.

+ Details

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X

- Details

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X

- Details

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X

- Details

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