I report results of over 850 microprobe
analyses of sulfides, sulfosalts and electrum from the Favona adularia-sericite
epithermal deposit of the Waihi district in the southern Hauraki Goldfield of
New
Zealand. Pyrite and marcasite from altered wall
rocks that enclose the veins are stoichiometric, with compositions of
FeS2, and no significant trace elements. In contrast, pyrite in veins
commonly contains appreciable As (up to 3.2 wt per cent), and locally contains
several tenths of a percent of Cu, Zn, Co, Ag and Sb. Vein pyrite may contain up
to 0.22 per cent Au, but Au contents do not show a positive correlation with As.
Limited electrum data indicate that it ranges from Ag0.47
Au0.53 to
Ag0.54Au0.41Cu0.01Zn0.04.
Chalcopyrite is stoichiometric CuFeS2, and most galena is PbS, but
some galena contains up to 4.4 wt per cent Se, which substitutes for S in its
lattice. The galena is not argentiferous; the highest Ag content is 0.45 wt per
cent Ag. Sphalerite averages 4 mol per cent FeS, but ranges up to 15 mol per cent. Tetrahedrites
[(Cu,Ag)10(Zn,Fe)2(As,Sb)4S13] show
variable substitution, but most are Cu- Zn- and Sb-rich. Veins also contain
aguilarite (Ag4SeS), stromeyerite (CuAgS), naumannite
(Ag2Se), and mckinstryite [(Ag,Cu)2S].