The presence of gold ores around the world is complex and variable. Essentially, gold occurs in nature both in the native state and combined with tellurium. The real ore of gold is native gold. It is important to mention native gold is generally alloyed with silver which may amount to 35 to 45%; it also often contains smaller quantities of the platinum group metals, iron, copper, lead, bismuth and mercury. Native gold occurs in part in situ in its original deposits, in part in beds of sand and gravel which have been formed by the destruction of the former. Gold of the first class is called reef-gold, of the second alluvial gold.
Reef-gold is generally found disseminated in quartz, accompanied by brown hematite in the upper portions (gossans) of the deposits, and by sulphides in the lower portions, especially pyrite, also arsenopyrite, blende and galena. It also occurs in very small quantities in many deposits that carry pyrites or blende. Alluvial gold occurs as dust, grains, scales, and larger pieces or nuggets in alluvial deposits, which form beds of sand, gravel or breccia either upon the surface (shallow placers) or at greater or less depths beneath it (deep placers), and which have been produced by the destruction of gold-bearing deposits. It also occurs in the sands of many streams and rivers, having been washed out of the rocks on their banks. Amongst the foreign substances with which alluvial gold is mixed may be named quartz, clay, mica, chlorite, serpentine, ilmenite, magnetite, chromite, garnet, spinel, zircon and platinum.
Gold prospectors know that important alluvial deposits have occurred, for example, on the western flanks of the Sierra Nevada in California, where they were 200 m in thickness and fill the valleys of Pliocene rivers. In the gravels of California, nuggets of 2,000 ounces, of Australia (Ballarat in Victoria) of 2,900 ounces, and of the West Indies of 42,000 ounces have been found. The most important localities for native gold are : Australia, especially the colonies of Victoria (Ballarat, Bendigo), Queensland (Mount Morgan, for a time the richest gold mine in the world, Gympie gold fields). West Australia (especially Coolgardie), New South Wales and New Zealand, in all of which countries it occurs both as reef- and as alluvial gold ; North America, especially the United States, and Canada (British Columbia, and Nova Scotia). Of the United States the principal places: California, especially on the flanks of the Sierra Nevada (reef and alluvial), Colorado, Nevada (Washoe, Carson river), Oregon, Idaho, Montana, Utah, Dakota, Arizona, Wyoming.
In South America gold is found in Brazil, the Guyana, and Peru ; in Africa, chiefly in the Transvaal, in South-West Africa, and the Gold Coast ; in Asia, in India, Turkestan, East and West Siberia. In West Siberia it occurs both in reef and alluvial deposits at Beresov, Miask, Troitsk, Goroblagodat, Tagil, Bisersk, Kishtimsk, as also in the districts of the Bashkires, Teptjares, and Cossacks; in East Siberia in the districts of the rivers Yenisei, Amur, Olekma, Witim and Kara. In Europe gold occurs only in relatively small quantity. It occurs in Russia, Italy (Pestarena), Finland and Norway. In England it occurs in Wales. In Germany, only in very low quantities in the sands of some rivers such as Rhine and Eder. Compounds of Gold with tellurium are important. These but rarely occur in any quantity; among them are Graphic Tellurium or Sylvanite (Au,Ag)Te, Foliated Tellurium or Nagyagite (Pb,Au), (S,Te,Sb)3, and White Tellurium (Au,Ag,Pb) (Te, Sb)3. These ores were detected at Nagyag and Offenbanya, in the Altai, in California, in Boulder County, Colorado, in West Australia, and other places.