Quartz veins from the Martha Hill epithermal gold-silver
deposit, Waihi, commonly exhibit crustiform banded textures. Visual differences
observed between bands are primarily the result of a 1 to 1500 m variation in
quartz grain size. Quartz band textures are dominated by anhedral interlocking
quartz mosaics, commonly associated with minor adularia and sulphide phases;
these textures are interpreted to be products of amorphous silica
crystallisation. The occurrence of rhombic adularia suggests that prolonged
boiling influenced parent fluids. In contrast, the presence of coarsely
crystalline bands, made up of subhedral to euhedral quartz grains, infers
primary crystal growth from solution; evidenced by the occurrence of
growth-zoned quartz within these bands. There is a narrow range of 3.3 in
18Oquartz between maximum and minimum isotopic values for
the deposit. Significant overlap in 18Oquartz values are observed between the Martha and
Welcome lodes. However, statistically significant and commonly systematic
differences do occur between individual bands analysed in most samples.
Temperature fluctuations may be the dominant factor responsible for observed
inter-band variation.