Cerro Matoso mine
|Production||41,000 t (40,000 long tons; 45,000 short tons)|
|Year of acquisition||2015|
The Cerro Matoso mine in northwest of Colombia is one of the largest open-pit ferronickel mines with the highest-grade lateritic nickel ore deposits in the world. The largest mine of South America, containing the largest nickel reserve in Colombia has been operated by Anglo-Australian multinational BHP Billiton since 1980. After 4 decades of mining with heavy metal pollution affecting especially local indigenous Zenu and Afro-Descendant residents the first study of a public health impact was published in 2015. BHP spun off Cerro Matoso in a new company. In 2018 the Constitutional Court of Colombia has ordered the mine to pay damages to local communities.
The mine is situated in the northwest of Colombia in the municipality of Montelíbano, Córdoba Department. The deposit was discovered in 1940. It developed over a Cretaceous peridotitic protolith, which is exposed in the form of an isolated elongated hill covering an area of about 4 square kilometres (1.5 sq mi). Ten distinct lithostratigraphic units have been characterized with the highest-grade lateritic nickel ore deposits in the world. The 108 megatonnes (106,000,000 long tons; 119,000,000 short tons) of ore contains 615,000 tonnes (605,000 long tons; 678,000 short tons) of nickel metal.
The hill comprises a holocrystalline rock of fine crystal size. Harzburgites and serpentinized dunites contain between 30 and 90% olivine, replaced by serpentinite.:11 Two sections through the weathering profile were sampled from an area of the mine with high (pit 1) and lower (pit 2) Ni grades. From bottom to top, the profile in pit 1 is weakly serpentinized peridotitic protolith, saprolitized peridotite, green saprolite (main ore horizon), tachylite (a Fe oxide horizon), black saprolite, yellow and red laterite. The sequence is capped by a magnetic to nonmagnetic ferricrete known locally as "canga". The succession in pit 2 is from serpentinized peridotite, saprolitized peridotite, brown saprolite, yellow and red laterite, and lacks the green saprolite ore horizon. All the units in pit 2 have currently uneconomic Ni grades.
The thickness of the units is highly variable, but most of the major horizons have maximum thicknesses of the order of tens of meters. Both pits contain abundant fault- and joint-related silicate veins. These veins contain the distinctive green mineral known as garnierite (actually pimelite, a form of nickeliferous talc) as well as quartz and chalcedony, and they can have a Ni content of up to 30% to 40%.
Nickel production in FY2008 was 41,800 tonnes (41,100 long tons; 46,100 short tons) of contained nickel and in 2014 was 41,000 tonnes (40,000 long tons; 45,000 short tons). In 2017, Colombia was the 11th highest producer of nickel in the world:112–113 with about 9% of its total mining value coming from nickel.
With exploration rights over 77,000 hectares (190,000 acres) in the main part of the Colombian nickel belt, Cerro Matoso has mining concessions containing reserves capable of sustaining the current[when?] level of production for at least 20 years. The mine has an estimated reserve life of 42 years, based on current[when?] production levels. BHP has expanded this significantly by building a third and fourth processing line and a heap leaching operation. BHP Billitons 2008 annual report stated proven ore reserves as under 25 megatonnes (25,000,000 long tons; 28,000,000 short tons), with probable reserves between 25 and 70 megatonnes (25,000,000 and 69,000,000 long tons; 28,000,000 and 77,000,000 short tons). Data acquired by the Colombian mining authority UPME indicated values in 2007 between 21 and 41 megatonnes (21,000,000 and 40,000,000 long tons; 23,000,000 and 45,000,000 short tons). As of 2013 Cerro Matoso had about 108 million tonnes of 0.57% grade ore nickel. The ore reserve has increased as a result of revised price forecasts, reducing the laterite ore cut-off grade used in the reserve estimation from 1.0% Ni to 0.6% Ni.
Environment and public health
Mine operations have been damaging the environment. Studying the area has been difficult as it has been ruled by groups such as the Popular Liberation Army, EPL and the Revolutionary Armed Forces of Colombia (FARC). The mine tailings or scum have been found to contain Fe2O3, Nickel oxide among other oxides, enstatite (pyroxene) and alpha-Alumina, Fe3+ clusters in a glassy matrix. Heavy metals such as mercury, zinc, copper, lead and cadmium have been found in rain water
Local people, indigenous Zenu residents have complained for decades about adverse health effects like an increase in neoplasms and respiratory, dermatological, ocular, and reproductive problems. The heavy metals have caused irreparable genotoxic damage in people living in the surrounding area. A small study examined the hair of people suspected to have hydroarsenicism and confirmed presence of arsenic.
In 2015, the Colombian Institute of Legal Medicine and Forensic Sciences issued the first study of the public health impact of the mine. It reported, that people living up to 15 km away near to Cerro Matoso, commonly had nickel in urine and blood samples, a high frequency of skin lesions and upper respiratory tract irritation. In March 2018, the Constitutional Court of Colombia sided with local residents and ordered the mine to pay for damages.
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