One of the early beneficiaries of the campaign against apartheid in South Africa was the Canadian Maple Leaf gold bullion coins.

Should sanctions harm some other South African mineral exports, Canada could also benefit. For instance, British Columbia coal mines might get new orders if South African bituminous coal exports suffer.That is not to say that Prime Minister Brian Mulroney had national self- interest in mind when he took a leadership position on sanctions at the recent Commonwealth meeting in London. But it surely is easier to be righteous about applying sanctions against apartheid when it isn't terribly expensive and might even be economically helpful to the domestic economy.

As a Toronto Globe and Mail headline put it after that meeting: ''Canadians Likely to Feel Few Effects From Sanctions Package."

Canada, it might be noted, has decided to fill a Canadian Wheat Board contract made in July for sale of $8 million of grain to South Africa. Indeed, one reason Canadian wheat sales went so well in recent years was its refusal to allow political issues (such as the Soviet invasion of Afghanistan) to interfere with business. In today's grim international grain market, Canadian farmers are undoubtedly happy to make every sale possible.

The Kruggerands were one of the early victims of the campaign against apartheid, a system that people against sanctions or for sanctions generally agree is abominable. It was no skin of the noses of governments - such as that of the United States - to ban the bullion coins. And it was a good symbolic protest of apartheid.

As a result, Yvonne Leblonde and her fellow workers at the Royal Canadian Mint here are especially busy. The government mint is running three shifts a day to keep up with orders for its gold coins. Mrs. Leblonde weighs the coins - thousands a day, lifting them out of a wooden tray with her rubber-gloves fingers, putting them on an electronic scale, taking them off again.

Faced with so many bans, South Africa decided late last year to cease minting Kruggerands and replace them with the Protea, another gold coin. If the Protea sells poorly, it won't put much pressure on South Africa. Since gold coins sell at only a small margin above bullion itself, the real cost to South Africa would not be large. The nation has no trouble unloading gold in bars.

In any case, last year Maple Leaf coins won 65 percent of the world market for "investment" gold coins, compared with 28 percent in 1984. So far this year sales are 13 percent above the same period last year.

"Virtually we are the market at this time," says Sallie L. Storey, sales manager for North America, the biggest market.

That won't last for long. The Perth Mint, which is owned by the state government of Western Australia, announced in June it will produce four gold coins, named Australian Nuggets, to compete for investors' money. They will go on sale in Australia in September and then elsewhere in the world.

More significant, the United States Mint began selling its four gold bullion coins Oct. 1. It has a symbol of liberty on the obverse side, family of eagles on the reverse side. Many Americans may prefer to buy their own country's coinage, though a whole family of eagles on a tiny coin may be overly crowded artwork.

Meanwhile, here in Ottawa, the Coinmaster 3, an English machine, is stamping out the various Maple Leaf coins (1 ounce, 1/2 ounce, 1/4 ounce and 1/10 ounce) at around 120,000 to 12,000 coins a shift on average. Being meant for investors and coin collectors, the gold blanks are struck only once, with the Maple Leaf design on top and the image of Queen Elizabeth II on the bottom. Numismatic coins are struck twice to get a clearer, deeper design.

The mint, now in temporary quarters, returns to its rehabilitated old quarters not far from Parliament Hill in the autumn. Visitors then will be able to view the minting operation from an elevated, glass-enclosed walkway.

For Canada, the minting of gold coins has at least two advantages. First, the coins consume some 65 percent of the gold produced in the country - 1,875,000 ounces last year compared to 1,002,000 ounces in 1984. That reduces any marketing problems for Canadian gold mines. Canada is the third largest producer in the world after South Africa and the Soviet Union.

Second, the operation is profitable. The 1 ounce coin, for example, has been retailing for around $350. The mint wholesales it at 3 percent above the value of the gold content and it retails with a 4.5 percent to 5 percent premium. Smaller coins have a higher premium. Whatever size coin, the mint makes sufficient to cover both the cost of manufacturing and promotion, and then end up with a good profit.

The typical buyer of Maple Leaf coins is male, over 38 years old, and has an investment portfolio of more than $100,000. He is likely to buy not just one coin but several for storage in a safety deposit vault or some other secure place.

One selling point Miss Storey emphasizes is that the Maple Leaf is the purest gold bullion coin available at 0.9999 fine. The gold is first refined by the mint, and then put through an electrolytic process.

Miss Storey spends about 50 percent of her time on the road keeping with the mint's distributors and major retailers in North America. Around the world there are 20 distributors in North America, Europe and the Far East - firms such as Johnson Matthey Bankers Ltd., Goldman Sachs, Bank of Nova Scotia and Credit Suisse. The number of retailers, including coin dealers, banks, and brokerages, is far more numerous.

The mint has been trying to broaden interest in the Maple Leaf coins by developing new markets. The coins were introduced into Hong Kong last September. A new 1/2 ounce coin was launched in Tokyo June 20. This coin

avoids the tax Japan imposes on gold coins of 1 ounce or larger. All the gold coins were introduced into Singapore June 26.

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