descloizite

Descloizite is a very rare mineral at Tsumeb. Klein (1938) observed that, in the upper levels of the mine, vanadium mineralisation was of economic significance only to a depth of 85 metres, with traces persisting to a depth of 160m (6 Level). Descloizite (and vanadinite) were described as very rare components of the vanadium mineralisation, with both minerals occurring in quantities greatly subordinate to mottramite. It is interesting that all specimens of descloizite in the Klein Collection are from Otavi Mountainland occurrences other than Tsumeb (Klein Collection catalogue, unpublished, Klein family archive).

Geier (1973/74) noted the very rare occurrence of descloizite in the second oxidation zone at Tsumeb and stated that cores of vanadinite are sometimes present in descloizite crystals.

Lombaard et al. (1986) confirmed that vanadium mineralisation (chiefly as mottramite) is concentrated at the top of the first oxidation zone (between surface and 4 Level) and noted a similar concentration at the top of the second oxidation zone.

Gebhard (1999) noted that vanadium mineralisation was restricted, essentially, to an interval between 50 m and 100 m below surface, and that descloizite was found only rarely in that zone.

Notwithstanding the rarity of descloizite at Tsumeb, there are several important (and prolific) descloizite localities nearby in the Otavi Mountainland. Not surprisingly, descloizite specimens from these other localities have commonly been sold or exported as part of consignments of "Tsumeb minerals" leading to incorrect locality attributions.

Descloizite is sufficiently rare at Tsumeb that specimens attributed to the mine should be regarded with caution unless there is clear supporting evidence in the form of associated minerals, matrix composition, etc.; even then, quantitative analysis is desirable to verify that the mineral is not simply a zinc-rich mottramite.

calcite; duftite; mottramite; tangeite (?); vanadinite; wulfenite

Descloizite is reported to form pseudomorphs after the following minerals: calcite (rare, doubtful validity); pyromorphite (rare, doubtful validity).