Bisha

Overview

The Bisha precious and base metals mine is located 150 km west of Asmara, Eritreea in East Africa. The mine is 60% owned by Nevsun Resources Ltd with the balance being owned by ENAMCO which is the Government of Eritreea’s company.

The Bisha deposit was first prospected in 1996 by a private Canadian company. It was first drilled in 2002.

Bisha is a conventional open pit mining operation that mines two distinct types of mineralization: a top layer enriched in gold and silver oxides that is being treated in a 2.0 million tonnes per year carbon-in-leach plant for the first two years; and, a copper rich layer that would be subsequently processed in a 2.4 million tonnes per year flotation plant.

The mine commenced construction in September 2008 and declared commercial production in February 2011. It is the only mine currently operating in the country. In 2011 it produced 330,000 ounces of gold.

Location

The Bisha mine is located 233 km by road west of Asmara in the country of Eritreea in East Africa. The nearest town is Akurdat located 43 km northeast. Access is by paved road from Asmara to Akurdat and from there on an all-weather unpaved road. The mining and exploration licences cover 86 square kilometers.

Eritreea, the ‘red land’, is a country located in the Horn of Africa. It is bordered by Sudan in the west, Ethiopia in the south and Djibouti in the southeast. It has an extensive coastline on the Red Sea. Its economy is based on subsistence agriculture.

Mine site area is located on a flat rolling desert plain situated along the western foot of the Central Highlands.

Climate is semi-arid with elevated temperatures year-round. The rainy season is from May to September and local rivers could be subject to spectacular flash floods. Mining activities are conducted on a year round basis.

Geology & Mineralization

The geology of the Horn of Africa is not well documented due to numerous armed conflicts that plagued the region since 1960s. The country of Eritreea is underlain by the western part of the Archean and Proterozoic rocks of the Arabian-Nubian Shield.

The Bisha deposit is underlain by low-grade metamorphic volcanic and sedimentary units. The mineral deposit is hosted by a complexly folded and foliated bimodal sequence of tuffaceous metavolcanic rocks.

Bisha is a large precious and base metal rich volcanogenic massive sulphide (VMS) deposit affected by a deep weathering process. The 60m - 70 m oxidized top layer is rich in gold while the underlying sulphide layer is made mostly of copper and subordinate zinc mineralization at a 2.4 million tonnes per year.

The Bisha Main Zone deposit extends for over 1.2 km along a north-trending strike and has been folded and separated into three different lenses.

The Harena deposit has a 400 m strike length and is a northwest dipping tabular body of sulphides.

As of December 2011, the estimated remaining payable production from the Bisha mine is 330,000 ounces of gold, 10,300,000 ounces of silver, 860,000,000 pounds of copper and 1,890,000,000 pounds of zinc.

Mining & Operations

Bisha is a conventional selective open pit mining operation.  Mining would firstly target the oxide ore at a 2 million tonnes per year rate for the first two years of operation.  It would subsequently mine the underlying supergene enriched zone and the sulphide zone.

Material is being blasted on 10 m high benches by drilling 140 mm and 102 mm diameter holes by using down-the-hole hammer drills. Loading is performed by two 7 cubic meters hydraulic excavators backed by an 8.4 cubic meters front-end loader. The mine employs 62 t rigid body mining trucks.

Process 

The 2 million tonnes per year oxide plant achieved commercial production in February 2011. The plant includes a primary crusher, SAG and ball grinding mills, cyanide leach/carbon-in-pulp (CIP) circuit, cyanide destruction circuit, refinery to produce doré, tailings thickener, tailings discharge system and the necessary reagent, water and air systems. 

Freshwater is sourced from groundwater.

The 2.4 million tonnes copper flotation plant and concentrate load out facilities are to be constructed on a 100 million budget and planned to be commissioned mid-2013. Thickened final copper concentrate is filtered and stored in bulk facility. Concentrate is trucked over a 300 km distance to the Red Sea port of Massawa for shipping to smelters.

Tailings would be thickened prior to being pumped to the tailings facility. A cyanide destruction circuit would further reduce the amount of cyanide in the tailings pond as to make it non-toxic to birds and wildlife. 

Environment & Community

The Bisha region is being used by local communities for grazing, agriculture and to access water resources. Altough the rmine are is sparsely populated the plan is to address the community's socio-economic needs and provide the basis for their enhancement of social and economic well-being.