HEAVY selling late in the day in Hang Seng Index futures caused a minor rout in the April contract in modest market activity. The contract fell 105 points to 8,555, on 13,000 contracts. There were nine contracts in May, which was marked at the close at 8,650. Sentiment turned weak in the afternoon after the Nikkei dropped off. Growing concern about the weakening United States dollar saw stop sell orders flood in after the market broke 8,580. April ended the day at a 32-point discount to the cash. Jardine Fleming said: 'Options traders were active in April puts.' Sentiment was mixed. 'Premium sellers sold 8,400 puts while those expecting the market to reach 8,000 bought 8,000/8,400 two-by-one ratio spreads,' said the brokerage. Thursday's open interest saw 33,758 contracts in April and 140 contracts in June. In options for April there were 4,452 calls and 4,496 puts. In June there were 2,327 calls and 3,709 puts. In September there were 864 calls and 866 puts. Implied volatility stood at 30 per cent. For September implied volatility was at 29 per cent in calls and puts. Dealers expect the market to take its cue from overseas capital markets next week, with US dollar woes dominating sentiment.