Gold Deposits in the Pacific Region
For many years the Pacific Region has been one of the main sources of gold deposits, but a relative minor producer in the world. The early gold production in the Pacific region was from alluvial gold deposits and with the time, this trend changed and the main gold deposits are found in hard rock deposits. Basically, the gold mineralization in the southwest comprises two major tectonic zones, the pacific ring of fire, related to tertiary to recent volcanic and hydrothermal activity; and the Australian block, whose gold production has been from Precambrian zones of western Australia, Northern Territory and South Australia, and from Palaeozoic Fold Belts of Eastern Australia. Basically, there are primary gold deposits of epithermal and porphyry characteristics, Au-Ag and Cu-Au deposits, respectively.
It is important to mention that primary gold deposits in the Precambrian areas are structurally-controlled veins or lodes and these deposits are considered the most prolific type of occurrence in the southwest Pacific region. Other important deposits are strata bound and lateritic deposits. Primary gold deposits of the Palaeozoic fold belts are of more numerous classes, and the most important of which in terms of production and potential are breccia pipes, saddle reefs and structurally controlled veins and lodes. It is possible to get gold deposits with different geological characteristics such as gold-bearing minerals, gangue minerals, host rock, grain size, gold content, among others. Also, the weather conditions, physiography and vegetation are important characteristics of the region. These characteristics have an impact on mining development, metallurgical performance, and economy of the project.
Without any doubt, gold has been one of the most important driving forces of the Pacific region, and more even since the dramatic increase in the gold price, in terms of currency. As a result the production of gold since the seventies was very interesting. Probably, this increase, spear-headed by Australia has been noted throughout the region from New Zealand and in the south to Philippines in the north, from Fiji in the east to Sumatra in the west. The early gold production was almost exclusively from alluvial deposits, which have become progressively less important since the first years of the XX century and of no significant economic importance since the twenties. Hard rock gold production comes from epithermal deposits, porphyry deposits, deposits in the Paleozoic fold belts, lode deposits in the Precambrian, Stratabound deposits in the Precambrian, and Lateritic. In the last years there has been a shift in the importance of different gold deposits. Whereas production from Precambrian and Paleozoic zones used to be far the major source of production, porphyry Cu-Au deposits are currently dominant in terms of production and the discovery of epithermal deposits is other important source of gold.