An experimental study of the mechanism of the replacement of magnetite by pyrite up to 300°C

Textural and compositional complexities resulting from coupled dissolution–reprecipitation reactions in geomaterials

“…This can lead to the pseudomorphic (isovolumetric) replacement of the parent phase by the product phase (Fig. 1b), assuming that the dissolution of the parent phase and the precipitation of the product are coupled in both space and time Putnis 2009;Qian et al 2010). Several key identifying features of such pseudomorphic replacements (also named 'interface coupled dissolution reprecipitation reactions', ICDR) have been highlighted by Putnis (2009) and can be seen in Figure 1, including:…”

“…The length scale of replacement can vary from the molecular (unit cell) level up to several meters, and is an important element of the mineral replacement texture (Qian et al 2010;Xia et al 2009a). Figure 5 illustrates the variety of textures obtained during the replacement of pentlandite by violarite.…”

“…Page 14/85 the µm-scale as in Figure 5f-i or in the replacement of magnetite (Fe 3 O 4 ) by marcasite (Qian et al 2010), to the complete uncoupling of anhydrite dissolution and gypsum (CaSO 4 ⦁2H 2 O) precipitation as seen in the Naica megacrystals, characterized by extremely slow precipitation rates compared to dissolution (García-Ruiz et al 2007;Otálora and García-Ruiz 2014).…”

“…78% pseudomorphic pentlandite + 3H + + 1.875O 2(aq) ⟶ violarite + 1.5Ni2+ + 0.75Fe 2 O 3 + 1.5H 2 O S -16.63% pseudomorphic (Xia et al 2009a) cryptoperthite ⟶ 0.54Ab 96 Or 04 + 0.46Or 87 Ab 17 (patch perthite) K-Na-Si-O -0.58% pseudomorphic (Norberg et al 2013) aragonite ⟶ calcite Ca-C-O 8.12% pseudomorphic with minor overgrowth (Perdikouri et al 2013) 54% ICDR with significant overgrowth (Zhao et al 2014b) 2pyrrhotite + 14H 2 S (aq) + 7O 2(aq) ⟶ 16pyrite + 14H 2 O Fe 15.70% pseudomorphic with minor overgrowth (Qian et al 2011) 2zoisite + rutile + quartz ⟶ 3anorthite + titanite + H 2 O Ti 18.78% pseudomorphic (Cruz-Uribe et al 2014; Kapp et al 2009) 2forsterite + 3H 2 O ⟶ lizardite + brucite Si 47.83% replacement with fracture generation (Kelemen and Hirth 2012; Plümper et al 2012) magnetite + 6H 2 S (aq) + O 2(aq) ⟶ 3pyrite + 6H 2 O Fe 59.80% replacement and overgrowth(Qian et al 2010) 3% ICDR with significant overgrowth(Zhao et al 2014a) …”

Contrasting regimes of Cu, Zn and Pb transport in ore-forming hydrothermal fluids

“…Gold is widely acknowledged to be carried as a bisulfide complex under most ore-forming conditions; common precipitation mechanisms include redox barriers (reduction of Au(I) complex to metallic gold); the destabilization of the Au(I)-bisulfide complexes for example via fluid-rock interaction and rock sulfidation (reducing the activity of sulfur by formation of Fe-sulfide minerals; e.g. Qian et al, 2010 and references in there); fluid mixing; boiling (H 2 S escaping into the vapor); and cooling.…”