The San Francisco Whig of September 1st, announces that gold has been discovered in New Zealand. The extent ot richness of the gold mines is not stated. The group of islands are 1,200 miles from Australia, and of volcanic origin, several active volcanoes being found in the Northern Island. The schooner Creeper, which brought the news to San Francisco, had laid on for Port Philip, and had already obtained a full complement of passengers, when the discovery of gold at Manukau, induced them to leave for the new placers. The troops which had been sent for by the Governor General of Australia were also withheld, as their presence was likely to be wanted