Lawrence, DM and Allibone, AH and Chang, Z and Meffre, S and Lambert-Smith, JS and Treloar, PJ, The Tongon Au deposit, Northern Cote d'Ivoire: an example of Paleoproterozoic Au Skarn mineralization, Economic Geology, 112, (7) pp. 1571-1593. ISSN 0361-0128 (2017) [Refereed Article]
The alteration haloes surrounding the deposit formed during three main stages: stage 1, early/distal potassic (biotite-K-feldspar-actinolite) metasomatism; stage 2, prograde clinopyroxene ± grossularitic garnet skarn; and stage 3, retrograde skarn consisting of epidote-clinozoisite-prehnite-albite and slightly later quartz-sulfide-Au. Garnets contain high Al and Ti, and the skarns have elevated Ni and Cr, reflecting the mafic composition of the host rocks. Proximal to peripheral mineral zonation patterns are defined by decreases in the ratio of garnet to pyroxene, increasing Fe in pyroxene, higher Au concentrations, and an increase in the intensity of retrograde alteration, seen as a change from white- to green-colored skarn. Spatially, gold-rich stage 3 alteration coincides with stage 2 intermediate diopside-rich skarn and distal hedenbergite-ferroactinolite skarn, whereas the proximal garnet-bearing skarn typically has much lower Au grades.
Fluid inclusions studies in the prograde skarn assemblages show primary, high temperature (>400°C), moderately saline (8–14 wt % NaCl equiv) H2O-NaCl-CaCl2 inclusions, with pressures estimated at 2 ± 0.5 kbar. The source of these fluids remains unclear, as plutonic rocks immediately to the west of Tongon intrude the skarn. U-Pb dating of hydrothermal titanite indicates the Au skarn formed between 2139 ± 21 and 2128 ± 21 Ma, 20 to 70 m.y. before the major episode of orogenic Au mineralization in southwest Ghana and western Mali. Dating provides further evidence that Au mineralization within the Paleoproterozoic rocks of West Africa craton occurred over several tens of millions of years through a variety of different processes.
|Item Type:||Refereed Article|
|Keywords:||gold, Tongan Au deposit, Au skarn mineralization|
|Research Division:||Earth Sciences|
|Research Field:||Ore Deposit Petrology|
|Objective Division:||Expanding Knowledge|
|Objective Group:||Expanding Knowledge|
|Objective Field:||Expanding Knowledge in the Earth Sciences|
|Author:||Meffre, S (Dr Sebastien Meffre)|
|Funding Support:||Australian Research Council (CE0561595)|
|Deposited By:||CODES ARC|
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