Derivative financial instruments (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure of derivative financial instruments [Abstract]

Disclosure of detailed information about hedge derivatives financial instruments [text block]

The table below presents the composition of open transactions included in the hedge derivative financial instruments as of December 31, 2017:

			Quotations
Period of settlement	MT		Fixed	Futures		Fair value
						US$(000)
January 2018		3,000	5,972 – 6,050		7,275		(3,788)
February 2018		3,000	5,972 – 6,050		7,260		(3,736)
March 2018		3,000	5,972 – 6,050		7,247		(3,693)
April 2018		3,000	5,805 – 6,050		7,259		(3,973)
May 2018		3,000	5,900 – 6,300		7,269		(3,484)
June 2018		3,000	5,900 – 6,325		7,277		(3,468)
July 2018		3,000	5,960 - 6,350		7,285		(3,359)
August 2018		3,000	6,520		7,290		(2,288)
September 2018		3,000	7,100		7,296		(580)
October 2018		3,000	7,200		7,300		(296)
November 2018		3,000	7,300		7,305		(13)
December 2018		3,000	7,300		7,309		(27)

		36,000					(28,705)

The table below presents the composition of open transactions included in the hedge derivative financial instruments as of December 31, 2016:

			Quotations
Period of settlement	MT		Fixed		Futures		Fair value
							US$(000)
January 2017		2,542		4,917		5,526		(1,548)
February 2017		2,270		5,001		5,530		(1,199)
March 2017		1,795		4,860		5,535		(1,208)
April 2017		500		5,720		5,536		92
		7,107						(3,863)

Disclosure of detailed information about financial instruments [text block]

Embedded derivatives held by the Group as of December 31, 2017 are:

Quotations

Metal

Quantity

Period of
quotations

Provisional

Future

Fair value

2018

US$

US$(000)

Copper

24,846 DMT

January – March

6,645.36 – 6,841.95

7,112.50 – 7,275.00

2,508

Gold

64,898 DMT

January – March

1,256.45 – 1,317.67

1,258.00 – 1,317.10

1,066

Silver

326,095 Oz

January – April

16.02 – 18.00

16.07 – 17.21

1,815

Lead

22,735 DMT

January – April

2,333.23 – 3,110.69

2,488 – 2,579.75

229

Zinc

54,603 DMT

January – April

3,103.72 – 3,275.47

3,226.50 – 3,343.50

1,806

Total asset, net

7,424

Embedded derivatives held by the Group as of December 31, 2016 are:

Quotations

Metal

Quantity

Period of
quotations

Provisional

Future

Fair value

2017

US$

US$(000)

Copper

29,121 DMT

January - April

2,985.28 – 5,824.00

5,535.76 – 5,642.25

397

Gold

15,370 DMT

January – February

1,139.75 – 1,145.90

1,151.00 – 1,179.40

481

Silver

17,124 Oz

January - April

16.32 – 19.35

16.42 – 16.66

(1,825)

Lead

23,636 DMT

January - April

1,871.58 – 2,380.60

2,017.00 – 2,080.00

(801)

Zinc

29,407 DMT

January – March

2,291.08 – 2,732.10

2,578.00 – 2,612.50

(172)

Other

15,082 Oz

396

Total liability, net

(1,524)