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HYDROUS SULFIDE MELTING: EXPERIMENTAL EVIDENCE FOR THE SOLUBILITY OF H₂O IN SULFIDE MELTS

Jeremy L. Wykes^,*

Department of Earth and Marine Sciences, Australian National University, Canberra, ACT 0200, Australia

John A. Mavrogenes

Department of Earth and Marine Sciences, and Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia

View larger version (78K): [in a new window]   FIG. 1. Backscattered electron image of a polished section from a typical galena capsule experiment (JW02-34). The galena capsule has been loaded with a pellet of sphalerite (sp) and troilite (tr).

View larger version (130K): [in a new window]   FIG. 2. Backscattered electron images from H2O-free melting experiments in the FeS-PbS-ZnS system. Abbreviations: gn = galena, sp = sphalerite, tr = troilite. A. Textures from experiment JW02-34 performed at 895°C, below the FeS-PbS-ZnS eutectic. B. Textures from experiment JW02-31 performed at 900°C. The onset of melting is indicated by the pockets of quenched melt formed between the troilite + sphalerite sample and the wall of the galena capsule. Small amounts of melt are present along tr-sp grain boundaries. C. Textures from experiment JW02-47 loaded with a tr-gn-sp sample pellet, as opposed to the tr-gn pellet of experiment JW02-31. This experiment dramatically demonstrated the presence of a small-temperature gradient within the capsule. Originally loaded with a sample geometry identical to that in Figure 1, the lower half of the sample, at temperatures high enough to melt, has migrated uptemperature toward the bottom of the capsule. D. Textures from experiment JW02-66, performed at 905°C. The 5°C increase in temperature results in almost complete melting of the sample.

View larger version (147K): [in a new window]   FIG. 3. Backscattered electron images from H2O-bearing melting experiments in the FeS-PbS-ZnS system. A. and B. Experiment JW02-56 at 865°C. The addition of H2O depresses the melting temperature in the FeS-PbS-ZnS system and produces patches of quenched melt with large vesicles, partially rimmed with galena. Much of the troilite and sphalerite has been recrystallized to textures similar to those in Figure 2C. Intergranular fluid pores are present throughout the capsule, confirming that the experiments were fluid saturated. C. Detail from (B), showing typical quench textures and small blobs of Pb-rich material within the quenched melt. D. Experiment JW02-50 at 875°C. This experiment contained two distinct types of quench textures. In the lower right corner of the sample there is a pocket of regular quench, whereas the rest of the sample consists of a coarse skeletal intergrowth of galena, sphalerite, and troilite.