Porphyry copper deposits are the world’s main source of copper and provide a large proportion of molybdenum, gold, rhenium and other important metals (Sillitoe 2010). Although much is known about these magmatic-hydrothermal deposits, the source of mineralising fluids and the mechanisms of fluid release and flow are poorly understood. From our field studies beneath a porphyry deposit in the Yerington District, Nevada, we have found textural evidence for fluid exsolution and mineralisation from aplite dykes which details these fundamental processes. Further, we use SEM-CL, EPMA and Total-IBA to characterise multiple generations of mineralising fluid flow through these dykes, particularly through measurements of titanium in quartz. From these data, our new conceptual model can explain the narrow focusing of mineralisation and high fluid/rock ratios necessary to form porphyry deposits. This has significant implications on our understanding of the formation of these ore deposits.
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