# Crixas gold mine in Brasil



## alshangiti (6 نوفمبر 2008)

Keywords
*Brazil*
*gold*
*underground*
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 Overview
The Crixas underground gold mine is located near the city of Crixas, in the Brazilian state of Goias (260 km northwest of Brasilia). Access to the area is by paved road, which links the city of Crixas and the Belem-Brasilia highway 120 km to the southeast. There is an airstrip suitable for small aircraft outside the city of Crixas. 

The mine operates two ramp access underground gold mines at the site in close proximity to each other, namely Mina III and Mina Nova, with a combined capacity of 740,000 t/y. The mine employs a total of 676 workers made up of 526 direct employees and 150 contractors. 

*Ownership Summary*
*Name*: Anglogold Ashanti
*Interest*: 50%
*Note*: public
*Name*: Kinross Gold
*Interest*: 50%
*Note*: public
_Reference: 31 Dec 2007_​The mining methods used are primarily mechanized cut-and-fill and room-and-pillar and ore is transported to surface by 25 tonne trucks. The operation runs 24 hours per day, 7 days per week. 

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Location - The Crixas mines are situated 3 km south of the city of Crixás in the Goias State of Central Brazil at Latitude 14°59'S and Longitude 50°59'W. This location is 260 km northwest of Brasilia, the country's capital. 

Access to the mine area is by paved road, which links the city of Crixas and the Belem-Brasilia highway 120 km to the southeast. There is an airstrip suitable for small aircraft outside the city of Crixas. 

*Location Summary*
*Nearest Landmark*: BRASILIA
*Distance from Landmark*: 260km
*Direction from Landmark*: NW
*Latitude*: 14 deg 59 min S
*Longitude: 50 deg 59 min W*


*Satellite Image*: The elevation of the Mina III mine portal is at 384 m a.s.l . Topography is slightly undulated with vegetation close to savannah type ('cerrado') with medium to small trees. 

The climate is characterized by two well defined seasons; the rainy season with heavy precipitation and the dry season with low humidity values. The rainy season is from October to March, with the remaining months hot and dry. Annual rainfall is approximately 1,500 mm. Operations run year round, with minimal disruptions due to weather. 

http://www.infomine.com/minesite/minesite.asp?site=crixas#top​


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 Property
The mining property is held by Mineracao Serra Grande (MSG), a Brazilian mining company. MSG holds two mining licenses that cover the area (1,946.89 hectares) of the two producing mines and an additional five orebodies. Major infrastructure consists of underground workings at Mina III and Mina Nova, a backfill plant, a mineral processing plant recovering gold, ore and waste stockpiles, a tailings dam, and tailings storage area. 

The gold deposits at Crixas are hosted by a sequence of schists, volcanics and carbonates occurring in a greenstone belt structural setting within the Upper Archaean Pilar de Goia's Group. Stratigraphy of the belt is dominated by basic and ultrabasic volcanics grading upwards into a more volcano-sedimentary dominated environment. 

*Deposit Summary*
*Deposit Type*: massive sulphide
*Primary Commodity*: gold

Gold at Mina III is associated with massive sulphides and vein quartz oreshoots. These are linear bodies with long axis lengths in excess of 200 m in places and plunging to the northwest at between 6-35°. The Upper and Intermediate Zone are dominated by massive sulphide bodies, whilst the Lower Zone is subdivided into a disseminated sulphide in the graphitic schist, and a high grade quartz orebody. At Mina Nova, the gold is associated with shallow dipping (6-10°) tabular bodies of disseminated sulphides. 

In Mina Nova mine and in the upper zones at Mina III the predominant sulphide minerals are arsenopyrite and pyrrhotite. In the Lower Zone at Mina III the pyrrhotite ******* increases and minor chalcopyrite can be observed. 

*Reserves Summary*
*Name*: Crixas
*Commodity*: gold *Class*: Proven + Probable
*Tonnage*: 5.3 Mtonnes
*Grade*: 5.08 g/t

*Note*: Containing 866,000 ounces of gold. _Reference: 31 Dec 2006_​

\The Corpo IV, Corpo V and Corpo Sul orebodies all occur in close proximity to the Mina III orebody and exhibit similar mineralogical properties to the Lower Zone at this mine. These orebodies are currently accessed from Mina III although mining has not commenced at Corpo V. 

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Operation
Both Mina III and Mina Nova are accessed by decline ramps, at gradients of 12 to 15%, sized to accommodate 25 tonne haulage trucks. Ore and waste are hauled to surface by truck from both mines to a common stockpile area for ore and waste, located to the north of the processing plant. Ore is stockpiled according to grade to allow blending of the feed to the processing plant. The operating schedule for both mines is three 8-hour shifts per day, 7 days per week, with a total of 341 operating days scheduled per year. This implies daily production rates of 1,364 tpd at Mina III, and 792 tpd at Mina Nova. 

At Mina III the main mining method is mechanized cut and fill using uncemented hydraulic backfill to recover moderately dipping quartz veins ranging in thickness from 1 meter or less, to several meters in the Lower Zone. Where the ore is thicker, pillars are left for support. Seven metre spans and four metre pillars are standard practice. Levels are spaced 50 m vertically, which results in a lateral distance of approximately 150 m between levels, along the dip. The overall mining sequence has been from the top, downward. *Mine Production Summary*
*Mine* - Crixas
*Capacity*: 740,000 tonnes/year
*Rate*: 790,000 tonnes/year
*Note*: Both the Mina III and Mina Nova
​ 

The mining cycle includes drilling, blasting, ventilation, dust suppression, scaling, mucking, rock bolting, and filling. Drilling is done using electric/hydraulic two-boom jumbos and blasting utilizes 80% anfo. The blasted ore is loaded into 25 tonne trucks by LHD or front end loader. The truck loading is done within the stope if dimensions permit, otherwise the ore is hauled to the main ramp by LHD, where loading takes place next to a remuck bay. 

Mina Nova is a relatively shallow mine, and there is a river flowing over it (Rio Vermelho). For this reason the geomechanical design of the mine is being carefully engineered and monitored. The main minng method is room and pillar. Underground access at Mina Nova is through the main ramp which has a section of 4.5 m x 4.2 m and has been driven to the northeast, following the gradient of the deposit.The dimensioning of the room spans and pillar widths varies depending on the thickness of the deposit. In the thinner areas, rooms incorporate spans of 8m and pillar dimensions are 3 x 3 m. Where deposit 1 is up to 20 m thick, rooms are dimensioned up to 13 m wide with 7 x 7 m pillars. These thicker areas are taken out by an initial cut followed by two benches to achieve the full height. 

Productivity in the mechanized room and pillar stopes averages 30 tonnes per man shift. 

http://www.infomine.com/minesite/minesite.asp?site=crixas#top​


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Process

The ore is hauled from the mines in Volvo A25 trucks and is stockpiled close to the feed hopper of the plant according to grade. Ore is then blended as it is fed by front end loader into the circuit. A vibrating feeder located at the bottom of a hopper feeds the primary crusher which is a jaw crusher operated in open circuit. Ore is then discharged onto a primary vibrating screen for a first classification. Secondary crushing is done in a hydrocone unit, operating in open circuit. Its product goes to a secondary screen that operates in closed circuit with the tertiary crushing unit. Crushed ore at minus 10 mm is stored in an 1,800 tonne silo. 

The grinding is single staged, wet, in closed circuit with hydrocyclones. Quick lime is added to the ball mill feed for pH correction. An Allis-Chalmers 3.65 m diameter by 5.2 m length steel lined ball mill is used, with a 1,343 kW motor. The circulating load is approximately 400%. Some 15% of the circulating load is directed to a Knelson centrifugal concentrator. The concentrate is fed to three shaking tables, after which it is sent to the fusion step. The hydrocyclones produce two products: the overflow with 25% solids and the underflow with 78% solids. The overflow (final product of grinding stage) feeds the thickener, and the underflow returns to the mill, being the circulation load. The final product of the grinding is approximately 65% passing 200 mesh (75 mm). The underflow from the thickener at 60% solids is pumped to the leaching stage. 

*Processing Summary*
*Facility* - Crixas
*Capacity*: unknown 
*Rate*: 790,000 tonnes/year
*Product*
*Commodity*: gold
*Quantity*: 194,000 oz
*Cost*: 198 US$/oz
​The leaching area consists of 16 tanks with 202 m3 capacity each. The leaching is done in two stages: pre-lime and cyanidation. Pre-lime takes place in tanks 1, 2 and 3. The contact time at the pre-lime is approximately 6 hours. The actual cyanidation occurs in tanks 4 to 16. The pulp is constantly agitated with the reagents in the tanks. The free cyanide and the pH gradually decrease along the tanks, being controlled at tank 15 at 200ppm of free cyanide and a pH of 10. The cyanidation contact time is approximately 26 hours. 



 The filtration circuit consists of two stages: primary and secondary filtration. There are seven rotary vacuum filters, 4.3 m diameter by 5.5 m length, and three vacuum pumps in the circuit. After primary filtration the cake, containing approximately 16% moisture, is fed to a primary repulping vessel, while the filtrate is pumped to a receptor tank. The pulp is pumped from the repulping vessel to the secondary filters. The process is repeated with two products being obtained: rich solution, that is pumped to a second receptor tank, and the final solid tailings, repulped, and pumped to the tailings pond. 

The Merril Crowe clarification and precipitation process is used consisting of clarification, air depletion from solution, gold precipitation with zinc powder, and subsequent precipitate separation using press filters. The precipitation area has 4 press filters, one operating at a time. The precipitate has an average gold grade of approximately 20%, and it is sent to the smelting building. 



 The fusion process consists of receiving and fusing the precipitate and gold concentrate originating from the press filters and shaking tables respectively. Every fusion produces a bullion weighing approximately 20 kg. The slag generated in the fusion is fused again to recover gold and then it returns to the crushing plant with a gold grade about 200 ppm. The fusion for bar production is done in an electrical induction furnace, where the bullions are fused and transformed into bars weighing approximately 10 kg each. Gold bars are sent to Mineração Morro Velho in Nova Lima-Minas, Gerais State, for refining


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