The relation between Cu/Au ratio and formation depth of porphyry-style Cu–Au ± Mo deposits

摘要: Constraints on gold and copper ore grades in porphyry-style Cu–Au ± Mo deposits are re-examined, with particular emphasis published fluid pressure formation depth as indicated by inclusion data geological reconstruction. Defining an arbitrary subdivision at a molar Cu/Au ratio of 4.0 × 104, copper–gold have shallower average (2.1 km) compared the copper–molybdenum (3.7 km), based assumed lithostatic from microthermometry. The correlation is primarily influenced variations total Au grade. Despite local mineralogical controls within some deposits, overall does not show significant predominant type Cu–Fe sulfide, i.e., chalcopyrite or bornite. Primary magma source probably contributes to metal endowment province scale individual but explain broad ratios formation. By comparison experimental analytical data, observed can be explained dominant transport Cu buoyant S-rich vapor, coexisting minor brine two-phase magmatic hydrothermal systems. At relatively shallow (approximately 3 greater confining likely precipitate molybdenum only, while sulfur-complexed remains dissolved dense vapor. Upon cooling, this vapor may ultimately contract low-salinity epithermal liquid, which contribute several kilometers above Au-poor porphyry Cu–(Mo) deposit. These findings interpretations imply that petrographic inspection density used exploration indicator. Low-pressure + systems favorable for coprecipitation both metals, leading Au-rich porphyry–copper–gold deposits. Epithermal associated such systems, derive their ore-forming components deeper source, include deeply hidden porphyry–copper Exposed high-pressure stockwork veins containing single intermediate-density inclusions, more prospective