Alteration phyllic

A poorly defined zone of phyllic alteration, which is characterized by a drop in the albite saturation index and an increase in the muscovite saturation index (when normalized to the Al content of the sample), either coincides with or lies within the sulfidic alteration halo. Absolute changes in K and Na concentrations in meta-sedimentary host rocks are dominated by lithological changes, and so the use of molar ratios is required to adequately define this zone by lithogeochemistry. This zone is not recognized in contact-metamorphosed deposits such as Maldon. 

The phyllic alteration zone coincides with a subtle but consistent shift in the dominant AlOH peak in the short-wave infrared spectrum ( 2210 nm) to slightly lower wavelengths, consistent with an inner white mica-ferroan carbonate mineral assemblage. A preliminary analysis of hyperspectral data over the visible to near infrared range suggests that ferroan carbonates may be detected but not reliably quantified. However, TIR data allow calcite and ferroan carbonate to be distinguished, and may also detect increasing Fe content in ferroan dolomite as mineralized structures are approached. 

Fig. 3. PER scatterplot of hypogene data testing feldspar (fresh igneous or potassic alteration) and muscovite (phyllic alteration) compositional controls.

The major rock units in the East-Kahang are made up of andesite, volcanic breccia, dacite, quartz-diorite, diorite and locally mineralized hydrothermal breccia (Fig. 2). Eocene andesite and volcanic breccias showing propylitic alteration are the oldest units in the area. They have been intruded by dacite, mostly showing phyllic alteration associated with weak copper mineralization. Quartz-diorite and dioritic... 

Taylor R.P. and Fryer B.J., 1980, Multi-stage hydrothermal alteration in porphyry copper systems in northern Turkey the temporal interplay of pocassic, propylitic and phyllic fluids. Can. f, Earth Sci, 17, 901-926. 

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