Gold grade variation and particle microchemistry in exploration pits of the Batouri gold district, SE Cameroon

Journal article

Authors / Editors

Shemang, Elisha

Research Areas

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Publication Details

Author list: Vishiti A, Suh CE, Lehmann B, Egbe JA, Shemang EM

Publisher: Elsevier

Place: OXFORD

Publication year: 2015

Journal: Journal of African Earth Sciences (1464-343X)

Journal acronym: J AFR EARTH SCI

Volume number: 111

Start page: 1

End page: 13

Number of pages: 13

ISSN: 1464-343X

Languages: English-Great Britain (EN-GB)

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Abstract

The Batouri area hosts lode-gold mineralization under several-m-thick lateritic cover. Pitting to bed rock on a geochemical Au anomaly defined from previous reconnaissance soil sampling identified five horizons ranging from saprock at the base to laterite at the top. Analysis of bulk samples from each horizon by fire assay shows that most of the horizons are barren although 119 ppb and 48 ppb Au values were obtained from one laterite horizon and one saprolite horizon, respectively, from two separate pits. All the horizons were panned and particulate gold was also recovered only from these two horizons. The gold grains from both horizons are morphologically and compositionally indistinguishable with rare quartz, pyrite and galena inclusions. The grains have irregular, sub-rounded, bean to elongated shapes and they show a remarkable core rim zonation. Electron microprobe analysis of the grains recorded high gold content in the rims (86.3-100 wt%) and along fissures within the grains (95.1-100 wt%). The cores are relatively Ag rich (11.8-14 wt% Ag) while the rims (0.63-13.7 wt% Ag, most of the values fall within the lower limit of this range) and fissures (0.03-5.02 wt% Ag) are poor in Ag. The low Ag concentration in the rims and along fissures is attributed to preferential leaching of Ag; a process recognized in gold grains and platiniferous alloys from alluvia. The core composition of the grains is similar to that of primary gold composition in the bedrock. These results show that gold in the soil is relic particulate gold derived from the primary source with no evidence of secondary gold precipitation in the weathering cycle. In all the pits no horizon was systematically enriched in gold suggesting there has been no chemical remobilization of gold in this environment. Rather the dispersion of gold here is in the particulate form. Therefore combining particulate gold features with assay data is relevant to exploration in such tropical environments. (C) 2015 Elsevier Ltd. All rights reserved.

Keywords

Cameroon, Chemistry, Core-rim-zonation, Finesses, Gold morphology, Soil profile

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