Exsolution depth and migration pathways of mineralising fluids in porphyry systems - examples from the Yerington District, Nevada

摘要

Porphyry copper deposits provide around 75% of the world's copper and are an important source of gold and other metals (Sillitoe 2010). One aspect of porphyry deposit models that is poorly understood is whether the mineralising fluids from which they form are derived from: (i) high-level copper-rich porphyry magmatic stocks; (ii) feeder chambers at mid-upper crustal levels; (iii) a lower crustal reservoir; or (iv) a combination of these in a transcrustal mush zone (e.g. Cashman et al. 2017). The high level porphyry stock is often assumed to be the fluid source as it is invariably mineralised and can usually be temporally and texturally linked to the mineralisation. It is unlikely, however, that enough fluid could be derived from such a limited volume of magma. It seems probable therefore that much of the fluid came from a deeper source, possibly 5-15 km, although how fluids are transported from such depths is poorly understood.