An experimental investigation of ore metals in silicate melt-volatile phase systems | Posted on:2002-07-04 | Degree:Ph.D | Type:Dissertation | University:University of Maryland College Park | Candidate:Frank, Mark Robert | Full Text:PDF | GTID:1461390011990298 | Subject:Geochemistry | Abstract/Summary: | | Vapor, brine, or vapor + brine magmatic volatile phase(s), MVP, were equilibrated with metallic gold and a haplogranitic melt at 800°C and 100 MPa. The goals of this project were two fold: (1) study the relationship between MVP composition and melt composition and structure, and (2) examine the concentration, speciation and partitioning of copper, gold, and iron in silicate melt-MVP-metallic gold systems. The starting composition of the NaCl-KCl-HCl-H 2O MVP varied from 3 to 70 wt.% NaCl (equivalent) with starting KCl/NaCl ranging from 0.5 to 1. Starting KCl/HCl was varied from 3.2 to 104 to evaluate element distribution as a function of the concentration of HCl in the MVP ; The data indicate that the equilibrium constant for the exchange of potassium and sodium between the melt and brine, (K, Na), decreased as the concentration of HCl in the brine increased. The results suggest: (1) reacts with the NaOH component in the melt to produce NaCl and H 2O; and (2) either the proportion of the NaOH component is greater than the KOH component in the melt, or NaOH is more reactive than KOH relative to HCl.; Analyses of fluids trapped at 800°C and 100 MPa indicate that high concentrations of gold, copper and iron can be transported by a MVP. Metal speciation was found to vary according to the H2S/HCl of the MVP. Copper and gold in a MVP with high H2S/HCl will be dominated by metal-sulfo species, CuHS and AuHS, respectively. Decreasing the H2S/HCl of a MVP to low values will change the speciation from metal-sulfo to metal-chloro complexes (e.g. CuCl and AuCl2H).; The results of this study indicate that gold and copper can be scavenged from a silicate melt by a high-HCl brine, although, a low-HCl brine is capable of transporting a considerable amount of gold and copper into an associated magmatic-hydrothermal system as well. Examination of the pertainment equilibria suggest that a significant amount of gold and copper can be transported by brines regardless of the fugacities of sulfur-bearing species, but that low-HCl brines require a high fugacity of H2S in order to transport large quantities of both gold and copper. | Keywords/Search Tags: | Gold, MVP, Melt, Brine, Hcl, Silicate | | Related items |
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