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Two major gold ore types are known to exist, i.e. the hydrothermal magmatic ones and the shear-zone related ones. The two types differ in many aspects, although the hydrothermal signature seems to be sometimes present in the last case.
Romania was known as a major producer of gold and the major deposits are in relation with Neogene magmatites of calk-alkaline affiliation. Both porphyry-copper-gold and hydrothermal vein deposits are known in the western part of Romania and the associated magmatites were considered first to be subduction-related (e.g. Radulescu & Sandulescu, 1973). New data suggest however that the Neogene magmas were generated in response to extension of the lithosphere, a fact based on new geochemical and isotopic data (Rosu et al., 2001). There are also many discussions concerning the unusual richness in Te of some ores (e.g. Sacaramb/Nagyag Au-Ag-Te deposit). Some authors favour a special evolution of hydrothermal systems (Cook et al., 2003) whereas others (Udubasa & Udubasa, 2003) present many arguments regarding the mobilisation of tellurium from older formations, during a long time processing of the area by at least five magmatic events, starting with the older ophiolitic rocks (140 Ma).
The Neogene hydrothermal ores have produced more than 90% of the gold in Romania. The remaining comes from both some small-scale shear-zone related ores in the metamorphics of the South Carpathians and the alluvial gold from this area and the Metaliferi Mts. (West Romania). The shear-zone gold ores exhibit a striking geochemical signature (Au-As) and no magmatic input can be argued.
In this respect it is perhaps important to highlight the significance of the scale of the shear-zones. It seems that the small-scale shear-zone (SSSZ) related ores are merely "pure" metamorphic products, with no obvious magmatic overprints and therefore with only remote relationships to the major tectonic settings. Their formation mainly depends on the existence of protores, as a rule orthoamphibolites and related rocks. No hydrothermal alterations in proper sense have been identified. The isotopic signature is limited as a result of a single source of elements. The large-scale shear-zone (LSSZ) related gold ores, e.g. in Australia, USA, India etc., extend over hundreds of km with a width of tens of km, with large scale tectonic overprints. Magmatic rocks such as Na-granites (Ramagiri, India) or diabases in other places show that the LSSZ bear some similarities to the hydrothermal ores, exhibiting both metamorphic deformation features and hydrothermal overprints (alterations, discordant forms of ore bodies). The isotopic signature is more diversified as a result of multiple sources of elements.
In a general classification of ore deposits the shear-zone related ones form a special class situated between the hydrothermal and metamorphic ores; the LSSZ bear many similarities to the hydrothermal ores, whereas the SSSZ seem to be practically "pure" metamorphic ores.
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