Geology of the Nguba Group-hosted Lonshi copper deposit in the Democratic Republic of Congo and exploration implications

Abstract

Lonshi is a newly discovered copper deposit located in the southeastern region of the Central African Copperbelt in the Democratic Republic of Congo. The deposit is hosted in the Nguba Group of the Katanga Supergroup. This paper analyzes the lithostratigraphy, controlling structures, ore host rock, and mineralization characteristics of the Lonshi deposit. The lithostratigraphy of the Lonshi area is comprised of the Mwashya sandstone of the Roan Group; conglomerate, dolostone, shale, mudstone, and siltstone of the Nguba Group; and conglomerate, pink dolostone, and siltstone of the Kundelungu Group. Geological structures identified within the mining zone encompass N-S and W-E trending folds, NW-trending fault, E-W sinistral shears, and various fractures and veins. The Lonshi deposit exemplifies a characteristic of hydrothermal stratiform mineralization, comprising two main orebodies situated within the Mwale conglomerate (lower orebody) and the underlying Lonshi dolostone (upper orebody). The ore was deposited during three mineralization stages, wherein the first hydrothermal stratigraphically-controlled stage deposited chalcocite 1, bornite, chalcopyrite, and pyrite. The structurally controlled stage 2 is subdivided into chalcocite 2 and bornite of stage 2a, and chalcopyrite, bornite, and native copper of stage 2b. Supergene alteration defining stage 3 resulted in the deposition of chalcocite 3, malachite, cuprite, azurite, and native copper 2. The gangue minerals associated with copper sulfide minerals consist of ankerite, feldspar, quartz, muscovite/sericite, kaersutite, barite, and illite. The sulfide minerals display zonation both vertically and laterally, transitioning from chalcocite to bornite to chalcopyrite to pyrite±sphalerite. Copper sulfide minerals occur as fine- to coarse-grained disseminations within the Nguba conglomerate andshow a replacement texture. The mineralizing fluids at the Lonshi deposit were likely enriched in Fe, Ca, Mg, Si, S, and Cu, with additional Mg contributed from the ore-hosting dolostone and Co and K from the ore-hosting conglomerate.

The Nguba Group at the Lonshi copper deposit shows distinct lithologies composed of black- to light-gray conglomerates and dolostone, which provide valuable insights for the discovery of new deposits. The observed mineral zoning, hydrothermal alteration, and multi-stage mineralizing events suggest favorable conditions for copper deposition. Targeting similar stratigraphic settings and alteration signatures in the vicinity of the Lonshi mine and in the Nguba Group could enhance the likelihood of discovering new deposits, particularly in areas exhibiting similar geological characteristics and structural features.