Summary of assemblages of alteration minerals, commonly used terminology, and the environment of formation. (Source : Atlas of Alteration; A Field and Petrographic guide to Hydrothermal Alteration minerals. Editors : A.J.B. Thompson& J.F.H. Thompson, MDD Series editor: K.P.E. Dunne, 1996).
|
Mineral Assemblage �(Key minerals are in bold) |
Standard Terminology |
Environment of Formation |
| Sediment-hosted massive sulphide | ||
| quartz, muscovite, siderite, dolomite, garnet, celsian, pyrrhotite, pyrite, barite | silicic | Pervasive replacement of footwall strata below massive sulphide; also of baritic facies of the sulphide body and less commonly in the hanging wall. Well developed within calcareous strata but more cryptic in siliciclastic strata. Can be mistaken for siliceous shale or chert. Occurs as "garnet quartzite" in high grade metamorphic rocks. |
| tourmaline, muscovite, quartz, pyrrhotite | tourmaline | Pervasive replacement of footwall strata bellow massive sulphide. Associated with abundant disseminated sulphide in shallow footwall. Limited to feldspathic strata. |
| ankerite, siderite, calcite, quartz, muscovite, pyrrhotite | carbonate | Disseminated carbonate, often as euhedral crystals, in the shallow footwall below massive sulphide and baritic facies. Disseminated ankerite/siderite can be very extensive within calcareous strata along major structures. |
| sericite, chlorite, quartz, pyrhotite, pyrite, albite | sericitic | Prevasive replacement of strata in broad halo around massive sulphide deposit; forms discordant bodies in structurally controlled vent areas. Occurs as potassium feldspar in high grade metamorphic rocks. Best developed in feldspathic strata. |
| albite, chlorite, muscovite, biotite | albitic | Pervasive repalcement of strata, and massive sulphides; more typically along structures and around mafic instrucion. Limited to feldspathic strata. |
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