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Comparative mineralogical and genetic studies on primary alunite from epithermal systems of Hungary
Published in Adam Piestrzyński, Mineral Deposits at the Beginning of the 21st Century, 2001
B. Bajnóczi, F. Molnár, K. Maeda, T. Vennemann
In the magmatic-hydrothermal environment the condensation of HCl and SO2 gas containing magmatic vapour into groundwater results in very acidic (pH=1-2) fluids at temperatures of 300-350°C (Hedenquist & Arribas 1999). The acidic fluids dissolve the rock-forming minerals. Presence of Ca-phosphate-bearing phase (woodhouseite) in the core of alunites from the Velence Mountains may indicate that dissolution of magmatic apatite by acidic fluids induce the precipitation of phosphate-sulphate minerals (Stoffregen & Alpers 1987). The dissolution and REE enrichment on the rim of phosphate-sulphate minerals may develop in the waning stage of hydrothermal alteration (Dill et al. 2000). After the complete dissolution of apatite the later formed minerals are Na-enriched alunites because at higher temperatures Na rather than K tends to be incorporated into alunite (Stoffregen & Cygan 1989).
Systems Based on AlP
Published in Vasyl Tomashyk, Multinary Alloys Based on III-V Semiconductors, 2018
The CaAl3(PO4)(SO4)(OH)6 multinary compound (mineral woodhouseite), which crystallizes in the rhombohedral structure with the lattice parameters a = 675 and α = 62°04′ or a = 696.1 and c = 1,627 pm in the hexagonal setting and the calculated and experimental densities of 3.003 g cm−3, is formed in the Al–H–Ca–O–S–P system (Pabst 1947).
Alteration and mineral zonation at the Mt Lyell copper–gold deposit, Tasmania
Published in Australian Journal of Earth Sciences, 2018
The Prince Lyell orebody is a large semi-vertical pipe that records an evolving hydrothermal fluid with alteration developed broadly symmetrically around the ore zones. At depth, the hydrothermal fluid deposited chalcopyrite, magnetite, pyrite mineralisation with associated phengite, chlorite ± biotite alteration, through to shallower levels where chalcopyrite and pyrite were deposited with associated muscovite ± chlorite alteration. A systematic variation in the white mica occurs both laterally and vertically from a core of phengite (Al-poor) to muscovite (Al-rich). This suggests that at depth, the hydrothermal fluid was of a neutral pH, reduced and hot, and as the fluid moved laterally and vertically towards the surface, it became more acidic, oxidised and cooler. The alteration at the Western Tharsis (Huston & Kamprad, 2001) and Glen Lyell deposits reflects increasingly shallow parts of the hydrothermal system with quartz–pyrophyllite ± topaz, ± zunyite ± woodhouseite assemblage with local bornite at the Western Tharsis deposit. The Glen Lyell alteration characterised by quartz–pyrophyllite–alunite represents the shallowest part of the hydrothermal system. The zonation for the type 1 chalcopyrite–pyrite pipe mineralisation is shown in Table 4. There are two types of phengite within the system: one is generated at depth from hot hydrothermal fluid, and the other represents the distal zone of the alteration system where the hydrothermal fluid has been neutralised by wall–rock interaction (Table 4). These results indicate that three main alteration types within the pipe-like orebodies are coeval, and they record the evolution of the hydrothermal fluid from deeper to shallower parts within the ore system.