Dioptase (J-79)

specimen number:
9273216

location:
Sanda Hills, Mindouli, Republic of Congo

description:

An exceptionally large lustrous and choice crystal of dioptase 2.7 cm in length part of a cluster of much smaller dioptase crystals. In super condition and outstanding for the species.

The Sanda Hill occurrences, situated within the Mindouli mining district in the Pool Department of the Republic of the Congo, represent a notable polymetallic deposit known for producing striking combinations of dioptase, plancheite, and crystalline quartz. Geologically, the mineralization is located along the structural margin of the Niari Syncline, hosted at the faulted contact between the Neoproterozoic stromatolitic limestones of the Schisto-Calcaire Group and the overlying Mpioka sandstones. Supergene enrichment along these regional, east-northeast trending fault zones produced complex, multi-phase copper-lead-zinc deposits rich in secondary copper silicates, carbonates, and lead minerals like cerussite. While indigenous communities engaged in localized copper extraction at Mindouli as early as the thirteenth century, formal industrialized exploration began under French colonial rule in 1905 with the founding of the Compagnie Miniere du Congo Francais. Large-scale corporate open-pit and underground operations at the Sanda open pit took place primarily from 1948 to 1960 before halting due to economic shifts, followed decades later by localized mechanized and artisanal specimen harvesting that concluded around 2019.

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