Abstract

In addition to the gold-bearing placers associated with deposits of the present drainage system, gold has been mined in the Tipuani region from a belt of Tertiary conglomerate ("cangalli") filling the deep channel of a former stream whose original steep gradient was further steepened by faulting and tilting during an episode of Andean uplift. The conglomerate consists of cobbles and boulders of slate, granite, and quartzite which together with finer-grained material are cemented by iron oxide; pay streaks have been found both close to bedrock (folded Devonian shales) at the bottom of the main and subsidiary channels, and at higher levels. High-temperature gold and tin lodes associated with granitic batholiths in the headwater region of the Tipuani river are assumed to be the source of metals in the cangalli.

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