Sericite Altered Granite

The whole rock k ar dates of k feldspar altered granite and sericite altered granite are both 126 6 ma.

Sericite altered granite. The poorer precision of the k ar dating left a great deal of uncertainty in defining the absolute age particularly as to whether some gold in jiaodong may have been older than previously determined for most of the other deposits. Xpl image 10x field of view 2mm plagioclase crystal altered by sericite in a granite. Sericite the fine grained form of muscovite or white mica occurs as a result of hydrothermal alteration processes in rocks throughout the cheviot hills. Most of the gold lodes are within the immediate footwall within quartz veined silica sericite carbonate altered greywacke and or granite with disseminated arsenopyrite.

Because it is generally made up of very small crystals its birefringence is irregular and generally low. Sericite is produced by the alteration of orthoclase or plagioclase feldspars in areas that have been subjected to hydrothermal alteration typically associated with copper tin or other hydrothermal ore deposits. Sericite replacing plagioclase in a metaluminous granite. All samples are recrystallised and most have a distinct foliation suggesting that the granite has been affected by.

Xpl image 10x field of view 2mm plagioclase crystal altered by sericite the brown material in a granite. Close examination of sericite reveals that at least some of it is fine grained white mica. Barrett and maclean 1999. Plagioclase crystal altered by sericite in a granite.

Sericite is grungy looking fine grained stuff that commonly replaces feldspars. Xpl image 10x field of view 2mm plagioclase crystal altered by sericite in a granite. The mount webb granite is hetero geneous comprising several types of unaltered granite sodic calcic altered granite sericite altered granite and aplite. Some narrow shear zone parallel zones of gold mineralization are present in the hangingwall graphitic phyllite.

Sericite is the name given to very fine ragged grains and aggregates of white colourless micas typically made of muscovite illite or paragonite. It is commonly seen in altered feldspar crystals particularly plagioclase associated with secondary minerals that give host crystals a cloudy appearance. Similarly in the intensely silicified zones at the turner albright vms deposit basaltic hyaloclastite has been progressively replaced by quartz sericite chlorite quartz chlorite and finally quartz sulfide zierenberg and others 1988. As documented above sericite hematite altered rdg occurs irregularly throughout all drillholes along the transect however the intensity of alteration increases with proximity to the odbc.

Most altered samples are from near the mount webb shear zone fig.