GLOBAL SEARCH FOR DIAMONDS — Global adds to diamond resource in South Africa

Following an extensive drilling program, California-based Global Diamond Resources (GDRS-O) has increased the resource at its Grasdrift alluvial diamond project in South Africa.

The company lifted the in situ gravel tonnage at its project along the Orange River to 81 million from 54 million tonnes — an increase of 50%. The new estimate is based on 650 percussion drillholes totalling nearly 10,000 metres. The reported grade for the deposit is about 1 to 1.5 carats per 100 tonnes; the average stone value, around US$600 per carat.

A previous landholder at the 2,300-ha property extracted about 25,000 tonnes of gravel from trenches and recovered some 250 carats, the average stone size being 2 carats.

Pieter van Wyk, Global’s chief consulting geologist, said this is typical of other low-grade alluvial diamond deposits found along the Orange River, which here marks the border between South Africa and Namibia.

The gravels at the Grasdrift were deposited in a small basin between two narrow canyons.

The resource at Grasdrift is confined to three terraces within the basin, and Global confined much of its drilling to the largest of these — the Intermediate terrace. The drilling density is highest near the mouth of the canyon, and decreases away from it.

The terraces consist of moderately sorted, coarse, clast-supported gravels with a silt-sand matrix. The clast size varies from a few centimetres to 1 metre in diameter.

Global has yet to explore the potential in the Upper and Lower terraces.

Should Global reach a production decision, access to the site for construction equipment is likely to come from the Namibian side of the Orange River. Grasdrift is in a remote location with few roads and other services available, though electricity is accessible from the South African grid.

The operation would likely mine about 160 tons of gravel per hour, or 3,200 tonnes per day, based on a 20-hour work day.

Regarding the mining of gravels at Grasdrift, van Wyk said two things are important to keep in mind. Identifying the barren sand beds from the paying gravels can minimize the amount of waste being processed. Also, by determining the shape of the bedrock surface just above the gravel, miners can gain easier access to potentially high-grade pockets of gravel.

“Potholes and plunge pools are often the site of rich diamond concentrations,” van Wyk said, “and knowing the underlying geology helps one locate them.”

The company recently sold 120 carats of large, high-quality gemstones recovered from its Caerwinning property. The price was US$58,148, or US$483 per carat.