Quimsacocha

Overview

The Quimsacocha gold-silver project is located in southern Ecuador, 30km SW of the city of Cuenca at an elevation of 3,600 m. 

A United Nations geological survey identified stream sediment anomalies in 1970s. Cogema acquired the tenements and optioned them out to Newmont in 1993. The latter was looking for a Yanacocha style deposit and when that failed to materialize they dropped their option. 

In 1999, Iamgold optioned 100% interest from Cogema by making payments and agreeing to a 5% NPI on future Quimsacocha production.

In 2004, Iamgold drilled a (discovery) hole that intersected 102 m averaging 9.1 g/t gold, 46.9 g/t silver and 0.4% copper which gave the company the confidence to extend the drilling program. 

Quimsacocha is a gold-silver epithermal deposit. 

A 3,000 tpd underground mine would be developed - it would extract 8.1Mt ore for 1.7M oz gold, 9.5M oz silver and 74.98Mlbs copper over an 8 years mine life. 

The ore is refractory and would be subjected to flotation followed by pressure oxidation that would result in producing cemented copper and gold/silver doré. 

Waste would be mostly reused as backfill material. 

Production is expected in early 2012.

Location

The Quimsacocha precious metal deposit is located in southern Ecuador. The equatorial country has a Spanish speaking population and is located on the western side of the South American continent on the shores of the Pacific Ocean. 

The mining project is 30 km SW of the city of Cuenca at an elevation of 3,600 m. Access to the property from Cuenca is by 40 km of paved road to the town of San Gerardo, 8 km of winding gravel road to the exploration base camp and 10 km of winding gravel road to the project. The project is located at an elevation ranging from 3,500 m to 3,900 m. 

Quimsacocha’s mining concessions belong to the ‘cloudy forest’ type and are characterized by frequent rain, hail and frost. Natural coarse grasses are predominant in the project area. 

Average temperature is about 6 deg C and the maximum temperature does not exceed 15 deg C.

Geology and Mineralization

Ecuador is made of a mosaic of terranes formed at the time of separation of the Central and South America. The terranes extend for hundreds of km in a NNE direction but are only a few tens of km wide; they are bounded by deep faults that favored the emplacement of some intrusive/subvolcanic bodies and acted as conduits for mineralization. 

Quimsacocha is an epithermal high sulphidation system with Au-Ag-Cu mineralization, formed by multiphase fluid injections associated with lithological and structural controls. 

Mineralization mainly consists of pyrite, enargite, barite and gold and it is better developed at the contact between tuffs and andesitic lava flows. 

The mineralized bodies are essentially flat lying. 

The deposit was then estimated to have an indicated Mineral Resource of 33 Mt at an average grade of 3.2 g Au/t and 24 g Ag/t for 3.3 million ounces of gold and 25.3 million ounces of silver at a cut-off grade of 1.0 g Au/t.

Mining & Operation

Quimsacocha is to be developed as a 3,000 tpd underground mine. The irregular geometry of the flat lying mineral deposit combined with poor ground quality resulted in the designation of the Post-Pillar Cut & Fill as the mining method of choice. 

Mineralization is to be recovered in horizontal slices advancing upwards. Mined out stopes are to be backfilled with paste tailings; 5mX5m pillars are left behind to provide support. Some 85% of the ore is going to be recovered this way. 

Roof bolting will be performed using a combination of roof bolter and conventional stoper bolting on a scissor lift platform. 

A six 50t dump truck fleet would be used to haul out the ore. 

The mining operation would be carried out by the company’s own personnel.

Processing

Quimsacocha ore is refractory in nature which makes processing a complex undertaking. 

A 3,000 tpd processing facility would be built close to the mine site at an elevation of 3,750 m. 

The ore is to trucked from the mine and discharged into a fixed grizzly to break coarse blocks; the ore is then fed to a Jaw Crusher (0.9 m x 1.2 m). The crushed ore will be stored in two 1,500 tonnes silos.Oreis extracted by two Apron feeders. The crusher will run for two shifts (14 hours per day), 7 days a week. 

A SAG (6.7 m x 3 m) mill was selected for primary grinding. A ball mill (4.6 m x 5.8 m) was selected for the secondary grinding unit. 

A gravity concentration circuit is considered to prevent loss of nuggets in the flotation circuit. 

The flotation circuit is simple and consists of rougher and cleaner circuits designed to reduce tonnage to be transported to the POX site. The rougher flotation will be done in 7 tank cells in series. 

Flotation tailings are sent to a paste backfill plant. 58% of the flotation tailing is planned to be used for underground backfill. The other 20% will be disposed of by pumping it as high density slurry to a tailings disposal area. 

The sulfide concentrate will be filtered and truck to the POX site for pre-treatment and valuable metal (gold and copper) extraction. The POX plant will be located nearGuayaquil, 300 km from the mill site. 

For the pressure oxidation circuit, an autoclave (3.6 m x 26 m) was selected to leach sulphides (iron and copper sulfides) and liberate gold and silver. The concentrate received at the POX site is re-pulped and fed to the autoclave. A CCD (6 thickeners) circuit is designed to separate pregnant solution and leached solid containing precious metals. The solution is sent to copper cementation and the slurry from CCD underflow containing precious metals to CIL. 

From the CIL circuit, loaded carbon is pumped to the stripping circuit to extract gold. The pregnant solution is sent to a refinery unit equipped with electro-winning and smelting.

This final step results in the production of bullions with high precious metals content.  

Doré bars will be sent to a gold refinery by air. Copper cement will be bagged and placed in containers and transported by road to theportofGuayaquilwhere it would be stored before being transferred onto a ship for delivery to a smelter. 

The mill will process 8,098,000 tonnes of ore over a period of 7.5 years. The average total production rate will remain steady at 3,000 tonnes per day for the life of mine at an average grade is 6.46 g Au/t and an annual production of gold is 204 685 ounces. Commercial production would begin in 2011. 

A total storage volume of 4.6 Mt is necessary for the development of the tailings and waste management facilities at the POX site.

Environment & Community

The “Paramo” region, where exploration activities take place, is completely uninhabited. This land is used as a communal area dedicated to pasture livestock. 

The nearest dwelling is located approximately 4 km from the mineralization site. The nearest town is Aguarongos, where IAMGOLD’S base camp is located. The closest populated centers are San Gerardo, 10 km south and Chumblin, 9 km southeast of the project. 

TheQuinuahuaycu River, which drains the Quimsacocha deposit area, is the watershed that is most likely to be impacted by the project. It is assumed that all types of waste e.g. tailings and waste rock, are highly reactive and will be acid generating. 50% will be used as paste backfill underground and the remaining 30% will be deposited on surface in the form of thickened tails or paste tails in tailings containment facilities. 

The plan is to dispose of the waste rock and tailings in a single cell underlined with a bituminous liner on a reworked clayed foundation.

A total workforce of over 200 employees is planned for the Mill, POX and assay laboratory areas.