No abstract

No abstract

No abstract

Figure 1. Phase stabilities in NaCl ؉ H 2 O fluid system, emphasizing two-phase coexistence surface (vapor ؉ brine; gridded by isopleths and isotherms; Driesner and Heinrich, 2003). Critical curve (heavy gray line at crest of two-phase surface) swings from high salinities at high pressure and temperature (P, T ) across to lower salinities at low P and T. Hot vapor-like fluid (V) of low to medium salinityoriginating from slightly above two-phase surface or coexisting with brine (B) along that surface-can be cooled and contracted to an aqueous liquid (L) without heterogeneous phase change provided that, during this stage of cooling, P remains above two-phase surface (arrows in 7% NaCl plane). Backface shows projection of critical curve (thick gray), halite saturation envelope (thin line), and one P-T path, including isobaric cooling interval (long arrow segment) modeled in Figure 2. ABSTRACTFluid-phase stability relations combined with thermodynamic modeling using fluid-inclusion analyses and new gold-solubility experiments lead to an integrated geological interpretation linking epithermal gold mineralization and porphyry-style ore formation to the cooling of hydrous magma chambers. The essential chemical requirement for gold transport to low temperatures is an initial excess of sulfide over Fe in the magmatic fluid, which is best achieved by condensing out Fe-rich brine from a buoyant, low-to medium-salinity vapor enriched in volatile S. This vapor can contract directly to an aqueous liquid, by cooling at elevated pressure above the critical curve of the salt-water fluid system. Physical and chemical conditions are matched when magmatic fluid is released through a gradually downward-retracting interface of crystallizing magma beneath a porphyry stock, predicting the consistent zoning and overprinting relations of alteration and mineralization observed in magmatic hydrothermal systems.

No abstract

No abstract

No abstract

No abstract