HYDROTHERMAL ALTERATION: ALTERATION MINERALS, ALTERATION STYLES, Conclusion and exploration implications
Corbett Short Course Manual
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| Common alteration minerals in hydrothermal systems. The Terry Leach pH versus temperature figure, updated from Corbett and Leach, (1998) for the Terry Leach Symposium in 2008. This figure illustrates groups of mineral assemblages described in thegeological literature and discussed herein. |
Abbreviations: Ab - albite; Act - actinolite; Ad - adularia; Al - alunite; And - andalusite; Bio - biotite; Cb -carbonate; (Ca, Mg, Mn, Fe); Ch - chlorite; Chab - chabazite; Chd - chalcedony; Ch-Sm - chlorite-smectite; Cor- corundum; Cpz - clinopyroxene; Cr - cristobalite; Ct - calcite; Do - dolomite; Dik - dickite; Dp - diaspore; Ep -epidote; Fsp - feldspar; Ga - garnet; Hal - halloysite; Heu - heulandite; I - illite; I-Sm - illite-smectite; K – kaolinite;Lau - laumontite; Mt - magnetite; Mor - mordenite; Nat - natrolite; Op - opaline silica; Pyr - pyrophyllite; Q -quartz; Ser - sericite; Sid - siderite; Sm - smectite; Stb - stibnite; Tr - tremolite; Tri - tridymite; Ves - vesuvianite;Wai - wairakite; Wo - wollastonite; Zeo - zeolite.
Hydrothermal alteration typically represents changes in mineralogy by interaction with the wall rocks of hydrothermal fluids related to the mineralising process, although some workers include gangue minerals deposited in conjunction with mineralisation as hydrothermal alteration. This section seeksto introduce the alteration minerals and define styles of hydrothermal alteration utilised in the following discussion of epithermal and porphyry mineralisation. The exploration implication is that alteration changes to the wall rocks adjacent to buried mineralisation identified by geophysical tools (magnetite introduction or destruction, and chargeable pyrite introduction) and zonation patterns in wall rock alteration minerals can be used as exploration tools to define drill targets.
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