W-bearing rutile formed during alteration of jarosite by resurgent hydrothermal fluids in the oxide zone of the Kori Kollo gold deposit. The rutile shows sector zoning in basal sections and well developed multiple growth zones, both defined in backscatter electron images by variations in the W content. The maximum WO3 content is 5.3 wt.% and W substitutes for Ti with double substitution of Fe to maintain charge balance. The causes of multiple growth bands are considered to be changes in externally controlled variables occurring in a shallow hydrothermal system. Whereas Ti is probably leached from biotite in dacitic rocks, the W is introduced by hydrothermal fluids.

Rare phases of the Au–Ag–Sb system were recognized in the Krásná Hora Sb-Au deposit (Sb 1.5–3 wt.%; Au 3–5 ppm), Czech Republic which correspond to auriferous dyscrasite (up to 7 at.% Au), auriferous allargentum (up to 34 at.% Au), and an unnamed phase with composition similar to the eutectics (E1, E2) of the experimental Au–Ag–Sb system. The dominant ore mineral is stibnite with rare native antimony, native gold and a Ag-Au alloy. Textural relationships are well established: stibnite (early) →gold → aurostibite → native antimony (late). Gold is present in four generations: Au-1 (0–15 at.% Ag) is the most abundant type; Au-2 (20–70 at.% Ag) forms thin rims along intra-grain boundaries of Au-1; Au-3 and Au-4 are rare and almost pure (∼0 at.% Ag). The formationof most of the Au-2 and of Au-Ag-Sb phases is associated with Ag-mobilization coupled with the Au-1 to aurostibite transformation via dissolution-precipitation and solid-state diffusion processes at temperatures <200°C.