Gold occurrences of the Woumbou–Colomine–Kette district, eastern Cameroon: ore-forming constraints from petrography, SEM–CL imagery, fluid inclusions, and C–O–H–S isotopes

• Published in: Mineralium deposita Vol. 57; no. 1; pp. 83 - 105
• Main Authors: Azeuda Ndonfack, Kevin Igor, Xie, Yuling, Goldfarb, Richard
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 2022; Springer Nature B.V
• Subjects: Calcite; Carbon dioxide; Carbonates; Chalcopyrite; Chemical precipitation; Chlorite; Earth and Environmental Science; Earth Sciences; Field investigations; Field tests; Fluid inclusions; Fluids; Gangue; Geology; Gneiss; Gold; Granite; Haematite; Hematite; Imagery; Isotopes; Metallogenesis; Mica; Mineral Resources; Mineralization; Mineralogy; Minerals; Muscovite; Orogeny; Pan-Africanism; Petrography; Petrology; Phase separation; Pyrite; Pyrrhotite; Quartz; Salinity; Salinity effects; Shear zone; Sodium chloride; Sphalerite; Sulfur; Sulphides; Sulphur; Zincblende; Cameroon; Woumbou–Colomine–Kette district; Cameroon; Mesozonal orogenic gold; Stable isotopes; Fluid inclusions
• ISSN: 0026-4598; 1432-1866
• DOI: 10.1007/s00126-021-01050-7

The Woumbou–Colomine–Kette district is located in the East Metallogenic Province of the Republic of Cameroon. Northeast- to E-striking splays of the regional Pan-African crustal-scale Sanaga Shear Zone control widespread gold mineralization. Gold occurs within local shear zones developed along granite-gneiss contacts, as well as within the margins of the Pan-African intrusions. Field investigations coupled with mineralogical and textural studies reveal two stages of gold mineralization. Stage 1 led to pyrite, chalcopyrite, sphalerite, pyrrhotite, bismuthinite, tellurobismuthite, galenobismuthite, and native gold deposition with quartz, sericite/muscovite, chlorite, calcite, and ankerite as gangue minerals. Stage 2 included the precipitation of pyrite, hematite, tellurobismuthite, and native gold. A SEM–CL study distinguished the two stages of quartz, as well as an early remnant barren quartz depositional stage. Two fluid inclusion assemblages (FIAs) with four types of fluid inclusions can be observed. The FIA 1 is aqueous-carbonic (±N 2 ±CH 4 ), with carbonate daughter minerals, which is related to stage 1 of the gold mineralization and composed of low salinity (~7.5 wt% NaCl equiv) H 2 O-CO 2 -NaCl (type 1), CO 2 -rich (type 2), and H 2 O-rich (type 3a) fluid inclusions. The inclusions provide evidence of episodic phase separation, with unmixing at P~2 kbar, T~300 °C, and at a paleodepth of ~7 km. The FIA 2 consists of aqueous (type 3b) fluid inclusions with a salinity of 0.2 to 11.7 wt% NaCl equiv and trapping temperatures between 205 and 245 °C. The δ 18 O quartz (+11.0 to +11.7‰), δD fluid inclusions (−46.2 to −40.9‰) and δ 13 C fluid inclusions (−4.9 to −4.1‰) for gold-bearing quartz veins suggest a metamorphic source for the ore-forming fluids, although some contribution from the mantle and/or magmatic source(s) cannot be ruled out. The δ 34 S (+6.5 to +7.0‰) for gold-bearing pyrites suggests a metamorphic source for the sulfur that transported gold and was involved in the precipitation of sulfide minerals. These data are consistent with a mesozonal orogenic gold deposit model for the Woumbou–Colomine–Kette district, which is an important part of the emerging greenfields exploration region for Pan-African orogenic gold and with the more significant targets defined by granite-gneiss contacts along NE- and E-striking shear zones.