Mottramite

specimen number:
2133384

location:
Tsumeb Mine, Otjikoto, Namibia

description:
Lustrous green crystallized mottramite across the top of matrix. In great condition.

The Tsumeb mine, located in the Otavi Mountain Land of northern Namibia, was a celebrated underground base metal operation renowned for its complex polymetallic deposit. Geologically, the orebody formed a steeply dipping, sub-vertical pipe-like structure hosted within the Neoproterozoic limestones and dolomites of the Otavi Group. The core of this pipe structure was filled with feldspar-rich sandstone breccia that underwent intense hydrothermal mineralization, creating massive concentrations of primary copper, lead, zinc, arsenic, and germanium sulfides. Due to an extensive internal drainage system facilitated by deep karstification, oxidizing groundwaters penetrated more than a kilometer below the surface, developing three distinct, deeply buried oxidation zones. Although local tribesmen had extracted surface copper ores for generations, formalized commercial mining commenced in 1897 under German administration and continued with various corporate restructurings until the economic exhaustion of the deep reserves forced the permanent closure of the mine in 1996.

Mottramite is a secondary lead copper vanadate mineral that crystallizes in the orthorhombic system, typically forming microcrystalline crusts, botryoidal coatings, or small, stout prismatic crystals. Geologically, it is a secondary mineral that forms in the highly oxidized zones of base-metal deposits, where primary lead and copper sulfides break down in the presence of vanadium-bearing solutions derived from the surrounding host rocks. The mineral commonly exhibits a distinct greasy to velvety luster, with coloration that spans a broad spectrum from dark forest green and olive green to nearly black or yellowish-brown. It was originally discovered and described in 1876 from Mottram St. Andrew in Cheshire, England, which represents its type locality, though it has since been documented in crystalline groupings from oxidized mining districts such as Tsumeb, Namibia, and Bisbee, Arizona.

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