Quartz Carbonate Fuchite Serpentinite, Age, Location. This rock has been altered by metasomatism. Metasomatism may occur via the action of hydrothermal fluids from an igneous or metamorphic source. In this case one of the new minerals to be formed is the fuchsite, a mineral similar to ordinary mica except that it contains chromium, which gives the fuchsite its green color. Another mineral introduced to the country rock was gold, in sufficient quantities to form a mineable ore deposit.
"Metasomatism is a mass transfer process, it is not restricted to the rocks which are changed by addition of chemical elements and minerals or hydrous compounds. In all cases, to produce a metasomatic rock some other rock is also metasomatised, if only by dehydration reactions with minimal chemical change. This is best illustrated by gold ore deposits which are the product of focused concentration of fluids derived from many cubic kilometres of dehydrated crust into thin, often highly metasomatised and altered shear zones and lodes. The source region is often largely chemically unaffected compared to the highly hydrated, altered shear zones, but both must have undergone complementary metasomatism." -THIS PARAGRAPH COURTESY OF WIKIPEDIA