Malachite after Barite

specimen number:
2292320

location:
Mashamba West Mine, Lualaba, DR Congo

description:

Neat cluster of what were once tabular barite crystals, these now completely replaced by crystallized green malachite. In good condition.

The Mashamba West Mine, situated in the Lualaba Province of the Democratic Republic of the Congo, is an open-pit copper and cobalt operation located within the western section of the Kolwezi Klippe. Geologically, the deposit belongs to the Central African Copperbelt and is hosted within the metasedimentary rocks of the Neoproterozoic Roan Group. These strata underwent intense folding and faulting during the Lufilian orogeny, creating structural traps where circulating fluids deposited primary copper-cobalt sulfides. Supergene weathering processes later oxidized these primary minerals near the surface, forming a rich oxide zone characterized by carbonates and silicates. Historically, the pit was opened in 1978 under the state-owned mining company Gecamines as part of the broader Dikuluwe-Mashamba complex. Following periods of economic instability and a suspension of operations in the late twentieth century, the concession was transferred and is now operated under the Sicomines joint venture. The mine is noted for producing significant industrial quantities of copper and cobalt, alongside specimens of malachite, cuprite, and cobalt-bearing calcite.

A pseudomorph is a mineral specimen that has undergone a chemical replacement process, whereby its original chemical composition is substituted by another mineral while the outward crystal shape of the original mineral is preserved. In the case of malachite after barite, tabular or bladed crystals of barite initially formed within a deposit. Over time, copper-rich solutions reacted with the existing crystals, gradually replacing the barium sulfate with malachite. The resulting mineral specimen retains the distinct crystal habit of the original barite, but it consists entirely of malachite.

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