The Barro Alto mineral resource is primarily saprolite overlain by laterites and extends for 35 km in an arc from southwest to northeast. The deposit is in the Barro Alto mafic-ultramafic complex, which is part of the Pre-Cambrian shield in the state of Goiás. The complex is composed of a sequence of serpentinised dunites and pyroxenites, enveloped by gabbros.

The mineralisation corresponds to the surficial weathered portions of the serpentinites. There are three types of saprolitic ore. The West type ore tends to have higher nickel grades and silica/magnesia ratios than the East type and Plain type ores.

The Barro Alto complex is bounded by metamorphic volcanic-sedimentary sequences (Ferreirafilho et al., 1992) and is a major mafic-ultramafic layered intrusion that was subjected to granulite facies metamorphism. It is composed mainly of gabbronorite, with minor dunite, peridotite, norite, gabbro, anorthosite and banded clinopyroxene-garnet amphibolite (Moraes and Fuck, 2000). In the complexes of Niquelandia and Barro Alto, lateritic weathering has formed important reserves of extractable Ni ore, representing around 2 million tons of metallic Ni (Raous et al., 2010). Ultramafic areas are characterized by a natural enrichment in heavy metals. In the case of the Barro Alto complex, this enrichment is mainly in Ni, however the Cr content has been reported as high as 6030 mg kg-1 (Ratié et al., 2015) and 46800 mg kg-1 (Raous et al., 2010), which is not high enough to be extracted, but potentially harmful for the environment. Mineral phases containing Cr include Cr-rich magnetite (Fe2+(Fe3+,Cr)2O4), chromite (FeCr2O4), talc (Mg3Si4O10(OH)2) chlorite ((Mg, Fe)5 Al[(OH)8 AlSi3O10]) and spinels (Oze et al., 2004).

No blasting is required to access the relatively soft laterite/saprolite ore, which is loaded by a backhoe hydraulic excavators with a maximum working bench height of 2.5 m. These load a fleet of trucks, which transport the material to a ROM stockpile.

The ore is dumped into a horizontal grizzly after which it goes through a three stage (primary, secondary, tertiary) process using two roll crushers followed by a Sandvik CH660 cone crusher, before conveying and stacking on a homogenisation stockpile; reclaiming to dryers subsequent and screening.

First metal from the Barro Alto ferronickel operation was produced on schedule in March 2011.

Conventional smelter-refinery technology is used to process the saprolite ore to produce ferro-nickel, which is a technology already used by Anglo American at its existing nickel operations.

At Barro Alto, ore is heated at very high temperatures in these two 185 metre rotary kilns in a process known as calcining, which removes moisture and water crystals from the nickel bearing ore and starts the 01 metallurgical process.

The project consists of an open pit mine and a ferronickel plant. The shallow pits forming the mine extend over an area 35 km long with a width of no more than 2 km. The plant uses a classical RKEF process to produce ferronickel.

The ore is dumped into a horizontal grizzly after which it goes through a three stage (primary, secondary, tertiary) process using two roll crushers followed by a Sandvik CH660 cone crusher, before conve ........