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Open File Report 41

Hydrogeochemistry of the Panglo Gold Deposit

Gray, D.J.

A hydrogeochemical survey of the Panglo Gold Deposit was conducted by sampling groundwaters in open drill holes, and from drainage holes in the Trial Pit. Waters were sampled from the three main geological environments of the area, namely shales in the south-east of the study area, mafic rocks, and ultramafic rocks.

The chemical characteristics of the water samples are closely correlated with the lithology in which the water was sampled. Waters derived from shales have relatively low concentrations in Au, the pathfinders, and most of the chalcophile elements analysed, whereas waters derived from mafic and ultramafic rocks have characteristic multi-element 'signatures'. Waters associated with mafic rocks are strongly enriched in Mn, Co, and Zn, and weakly enriched in Cu and Ni, whereas waters associated with ultramafic rocks are enriched in Ni, Cr, Bi, Sc and Ag. Using these data, water samples could be distinguished into geological groupings by using chemical compositions alone.

Chemical data also suggest major variations in the degree of weathering and leaching within the sample area. Waters in the northern part of the study area are highly acidic and oxidising, and have anomalously high concentrations of Au, Br, Fe, Mn, Co, Zn, Cu and Ni. Dissolution of Au is primarily controlled by the redox status of the solution. Elevated Eh levels are caused by Mn oxidation, permitting the oxidative dissolution of native Au and its mobilisation by either the chloride or the iodide complexes. Dissolution of Au as the iodide complex occurs as a consequence of the relatively high concentrations of I at this site. Such a Au mobilisation mechanism has not, in the author's experience, been previously documented for groundwaters. The concentration of dissolved Au is high, and would represent a reasonable exploration method at this site.

Last updated: Thursday, January 06, 2000 08:32 AM


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