EXPLORATION 1999 — General Minerals drills iron project in Chile

At the Imam iron prospect in central Chile, General Minerals (GNM-T) has begun drilling the first of five holes designed to test a new geological interpretation.

The Iman anomaly was first discovered by Bethlehem Chile Iron Mines in a 1963 aerial magnetic survey. The survey used a line spacing of 1 km to outline an elongated bull’s-eye covering 12 sq. km and which suggested significant magnetite mineralization. However, General Minerals President Ralph Fitch says the anomaly has never been adequately tested.

Drilling will test the anomaly in accordance with a reduction-to-pole interpretation that shifts it 1 km southwest of the position given by the raw data.

In August and September 1998, General Minerals completed ground magnetic and induced-polarization (IP) surveys over the area covered by the 1963 airborne survey. Using a line spacing of 200 metres, crews took measurements every 20 metres on each line. With the help of geophysicist Jack Skokan, General Minerals recalculated the magnetic data to determine the location of the anomaly. Skokan made a reduction-to-pole calculation based on the latitude of Iman relative to the magnetic equator.

Skokan also modeled the anomaly as a magnetite body measuring 500 by 1,000 metres and up to 500 metres deep.

General Minerals collared its first hole smack in the middle of the anomaly, drilling the hole at an angle of 80 to the north, because the IP survey indicated that the rocks dip steeply to the south. The company will step out 200 metres along an east-west line for each of the next four holes, totalling 2,500 metres. A percussion drill will penetrate more than 100 metres of gravel before switching to core for the bedrock below.

“Iman is an iron deposit,” says Executive Vice-President Lawrence Dick, “but there remains the question of grade and economics.”

The company believes that grades of 40-45% iron would be considered economic. Results of the drilling are expected in the next few months.

Iman covers 71 sq. km near Vallenar in Chile’s Region IV. While adjacent to the company’s Productura copper-gold property, Iman is in the Chilean Iron belt, a north-trending belt of magnetite mines and mineralization associated with the Atacama fault, which stretches from La Serena to north of Copiapo.

For the area, Iman is one of the largest magnetic anomalies that does not have an iron mine associated with it, says Fitch.

The Atacama fault has been the locus of magmatic intrusion. Magnetite mineralization is typically hosted in Cretaceous diorites intruded into Mesozoic sedimentary rocks. The sequence is covered by the regionally extensive Atacama gravel.

Chilean iron producer Compania de Acero del Pacifico (CAP) was the first to drill at Iman, in 1969. Its only hole, collared in the centre of the original anomaly, intersected uneconomic grades of magnetite. With the reduction-to-pole calculation, that hole appears to be around the edges of the new anomaly.

In 1996, another company re-evaluated the property with three more holes, using a line spacing of 1 km. Its first hole, which twinned the hole drilled by CAP, encountered modest grades of iron ore. Starting at a depth of 160 metres, the hole intercepted 260 metres of more than 30% iron, including higher-grade intervals of 6 metres grading 53% iron and 18 metres of 46% iron.

The second hole, drilled 1 km south of the first two, hit 15.5% iron over 398 metres. The third hole, 700 metres west of the first hole, hit 147 metres of 12% iron.

Iman is situated at a low elevation, 11 km from Vallenar. Two rail lines and a power line pass through the property, while port facilities are 46 km away at Huasco.

Chile is already a significant iron-ore producer. CAP operates the El Algarrobo iron mine, 45 km southwest of Vallenar, while the Los Colorados mine is 40 km to the northwest. The El Romeral mine is 20 km north of La Serena. However, all the iron mines in the region occur much closer to the surface and were easier to locate.

Elsewhere in Chile, General Minerals is exploring for copper and gold. It is currently drilling at the Escalones porphyry project southwest of Santiago, and recently joint-ventured Productura with Teck (TEK-T).