BELGIUM DETAILS PRICING PLAN FOR ECU GOLD COIN The 50 European Currency Unit gold coins which go on sale tomorrow in Belgium will be priced at a premium of seven pct to the value of the gold they contain, a Finance Ministry spokesman said. The price will be calculated daily, based on the daily gold fixing in London. Belgium is minting an initial 50,000 gold coins to celebrate the 30th anniversary of the European Community's founding Treaty of Rome, but final production is expected to be around 200,000. Each 17.27 gram coin will contain 55 grams of fine metal. Two mln silver coins, face value five Ecus, will be sold at 500 francs each.