Name: Andorinhas mine.

Location: The Andorinhas mine is located in the central eastern area of Para state, in Brazil.

Controlling Company: Troy Resources, through its wholly owned subsidiary Reinarda Mineração (RML).

Brief History: Companhia Vale do Rio Doce (CVRD) undertook regional reconnaissance and identified two important base metal geochemical anomalies at Andorinhas in 1973. Two years later, CVRD discovered gold mineralisation at Babaçu by using field mapping, and at Mamão and Lagoa Seca using soil sampling.

CVRD filed a new mining licence application in 1991, following a drilling campaign in 1986 to evaluate the remaining resources, estimated at 1.5-million tonnes of ore at 8.8 g/t of gold.

According to the technical report published in 2007 for the mine, illegal miners, or garimpeiro, mined multiple surface zones of oxide mineralisation from 1982 to 1989 at Andorinhas, and excavated an underground ramp at the Melechete deposit at Mamão. An estimated 626 000 t of ore grading 8 g/t of gold was mined, producing 160 000 oz of gold.
From 1998 to 2004, illegal miners also reworked tailings from the Mamão ramp.

From 1994 to 1998, CVRD entered a joint venture (JV) with Southern Star Resources (SSR), a wholly owned subsidiary of Golden Star Resources. SSR conducted 15 000 m of diamond drilling and subsequently withdrew from the JV.

Reliance Minerals acquired an option to buy the property from CVRD in 2004, and undertook a scoping study and resource and reserve estimate. The following year, Consolidated Minerals took over Reliance.

Agincourt acquired the property from Consolidated Minerals in 2005 and completed 6 000 m of drilling at Mamão and Lagoa Seca.

In November 2006, Agincourt sold the property to Troy. Troy then established RML to operate the project. RML applied for trial mining and environmental permits and for an extension to the exploration permits.

Brief Description: The Andorinhas mine hosts two gold deposits – Mamão and Lagoa Seca – within concessions that cover about 20 000 ha. The gold mineralisation occurs as several deposits, hosted in Archaean greenstones of the Carajás minerals province. The deposits have been worked in the past as opencut and underground operations by illegal miners.

Geology/Mineralisation: The project lies within the Andorinhas greenstone belt. This is a typical volcano-sedimentary sequence, with a basal sequence of felsic-intermediate metavolcanics, interbedded with metasedimentary rocks and an upper mafic metavolcanic dominated sequence that is metamorphosed to upper greenschist facies.

There are two mineralised trends – the Mamão-Babaçu and the Lagoa Seca. The shear zones follow the regional east-northeast trend.

Mineralisation is of two differing styles: quartz/carbonate/sulphide shear hosted reefs, in the Mamão area, and disseminated sulphide mineralisation hosted within a broad shear zone at the Lagoa Seca area.

Reserves: Total probable reserves at Mamão underground in 2014 were 70 000 t grading 5 g/t of gold. Probable reserves at the Corujá pit were estimated at 86 000 t grading 5.8 g/t. Proven reserves at the Lagoa Seca stockpiles were estimated at 52 000 t grading 1.4 g/t of gold.

Products: Gold.

Mining Method: The mine uses two mining methods – shrink stoping and cut and fill.

Major Infrastructure and Equipment: Access to the Andorinhas mine is through a 5 m × 5 m ramp decline system. The mine operates three drill jumbos – an Atlas Copco 104, 251 and a twin boom 282 for primary development.

Ore and waste are loaded using a fleet of load haul dumpers, including a Toro 301, ST2G and a Caterpillar R1600G.

The mine also runs two underground diamond drill rigs – a Boart Longyear LM75 and Diamec U4.
The processing plant operates a conventional ball mill and carbon-in-leach circuit, which processes an average of 70 t/d. Gravity gold is processed through a Knelson concentrator and an Acacia plant, with recovery averaging 92%. Tailings are treated by an INCO detoxification circuit before disposal in a tailings dam.
Prospects: Underground mining activities are decreasing in line with the mine’s scheduled closure in the March quarter of this year.

Contact Person: Company secretary Stacey Apostolou.

Contact Details:
Troy Resources,
tel +61 8 9481 1277,
email troy@troyres.com.au, and
website www.troyres.com.au.