Evaporation losses in Australia are enormous, and this fact detracts greatly from the effectiveness of water stored in surface reservoirs. Evaporation losses from open-water surfaces in areas having less than 10 inches of rainfall are estimated to average about 7 feet per year. Shallow reservoirs are almost useless in arid country, for during a 2-year drought practically all the water would be lost by evaporation alone. One of the great advantages of artesian basins is that they are free from evaporation losses.
STOCK WATER SYSTEMS
In Victoria the total area of land supplied with water for domestic and stock purposes and for irrigation (exclusive of metropolitan areas) amounted to 15,376,000 acres. The irrigated crop land amounted to 657,000 acres, but much additional pasture land was watered. The Wimmera-Mallee Domestic and Stock Water Supply System provided water for 12,000 farmers living in the drier parts of the state and occupying nearly 15,000,000 acres of land. Thousands of miles of ditches deliver water to storages on these holdings at selected times of the year.
The occurrence and distribution of mineral resources in Australia are obviously related to the geologic character of the continent. The widespread distribution of Paleozoic and Precambrian rocks in the western two-thirds of the continent, along with isolated patches in the east and in Tasmania, accounts for the importance of Australia's resources of gold, silver, lead, tin, copper, and related minerals. The fact that these ancient rocks lie exposed at the surface over wide areas has facilitated prospecting. The sparseness of vegetation in most of these areas has likewise made mineral discovery easy, although in places surface deposits of sand have been a handicap. Some minerals, such as gold and tin, have accumulated in placer deposits after the disintegration of the source rocks.
PRECAMBRIAN MINERAL DISTRICTS
The Western Australian gold fields, from Halls Creek, Pilbara, and Marble Bar in the north to Kalgoorlie and Phillips River on the south, are related to surface exposures of Precambrian rocks. Minor occurrences of copper, chromium, lead, and tin also are involved.
The Spencer's Gulf-Broken Hill mineral district of South Australia and New South Wales owes its existence likewise to the presence of these ancient rocks. The lead-zinc deposits of Broken Hill, the formerly important reserves of copper at Burra, Kapunda, and WallarooMoonta, and the rich iron ores of the Iron Knob district lie near the southeast corner of the ancient Western Plateau.
Within the north margin of the plateau are the Yampi Sound iron deposits, the Kimberley gold fields, the copper deposits of Cloncurry, the lead-zinc-copper ores of Mt. Isa, and many smaller scattered deposits of gold, silver, tungsten, lead, and tin in Northern Territory.
PALEOZOIC MINERAL DISTRICTS
The Eastern Highlands of Australia contain Paleozoic rocks that are mineralized from York Peninsula on the north to Tasmania in the south. The highlands of Queensland and northeastern New South Wales are almost continuously mineralized. Tin and gold are important in the north at Herberton and Croydon; gold and copper are more significant at Mt. Morgan; and tin is important on the New England Upland. The Cobar uplift in New South Wales has gold and copper, and the gold deposits of Bendigo and Ballarat of Victoria are well known. The older mineralized rocks of western and northeastern Tasmania have produced copper, lead, zinc, tin, and other metals.
Although Australia does not rank among the countries having great reserves of mineral fuels, it does have sufficient coal deposits to meet the needs of the southwest Pacific region for many generations. The presence of important supplies of natural petroleum has still to be demonstrated. Bituminous coal occurs principally in several large basins in southeastern Queensland, between Bowen and Brisbane, and in eastern New South Wales, between Port Stephens and Port Kembla. Large deposits of lignite occur in the Gippsland district of southern Victoria. Small deposits of bituminous coal exist in eastern Tasmania, at Collie, Western Australia, and elsewhere. Some lignite is found at Leigh Creek, South Australia. The bituminous coal resources of Australia are estimated to be about 10,000,000,000 tons, and the lignite reserves are believed to be as much as 40,000,000,000 tons.