Mineralogical and geochemical constraints on gold enrichment in the Tchiquele Epithermal System, Southern Angola

• Author(s): Kumoleha, A. ; Nogueira, P. ; Pimenta, P. ; Marinho Reis, A. Paula
• Date: 2025
• Persistent ID: https://hdl.handle.net/1822/98236
• Origin: RepositóriUM - Universidade do Minho
• Document Type: Other
• Language: English
• Contributor(s): Universidade do Minho

Description

This study investigates the Tchiquele gold deposit in south-ern Angola, a geologically prospective region with limited prior research despite its recognised mineral potential. By integrating geochemical, mineralogical, and metallographic analyses, the research aims to provide new insights into the metallogenetic evolution of the area, contributing to the broader understanding of hydrothermal gold systems in sub-Saharan Africa. The specific aims of the study are to: (i) characterise the host lithologies and mineralised structures; (ii) define the geochemical signature of the deposit; and (iii) identify the mineral phases associated with gold mineralisation. Two field campaigns yielded 97 samples, encompassing both host rocks and mineralised material. Selected specimens were analysed using transmitted-light petrography and metallographic microscopy, supported by X-ray diffraction (XRD), scanning electron microscopy (SEM), and whole-rock geo-chemical analysis of 45 samples to determine mineralogical assemblages and trace element distributions. Gold concentrations range from 0.7 to 80100 µg/kg, with an average of 5744 µg/kg, and a positively skewed distribution, consistent with nugget effects and localized enrichment. Geochemically, gold correlates with Fe, S, Bi, Pb, Cu, and Ag, elements commonly associated with hydrothermal sulphide mineralisation. Pyrite is the dominant sulphide phase, frequently containing inclusions of chalcopyrite, galena, bismuthinite, hematite, and Au-Ag selenides, indicative of low- to intermediate-sulfidation epithermal environments. These assemblages and their microtextural relationships suggest a polyphase hydrothermal evolution, marked by episodic fluid influx and subsequent overprinting. Gold occurs mainly as inclusions within pyrite and quartz, with fractures often filled by hematite, pointing to late-stage supergene alteration. The presence of visible gold in quartz and its consistent association with sulphides and oxides supports a model of hydrothermal mineralisation under oxidizing to transitional redox conditions, characteristic of low sulfidation epithermal systems. However, due to the limited number of representative samples, interpretations should be approached with caution. Further investigation is required to fully resolve the sequence of mineralizing events responsible for the formation of the Tchiquele deposit.