Gold in Stream Sediments from the Sardinia Crystalline Basement (Italy)

From the first half of the 1970s to the early 2000s, more than 33 000 samples of stream sediments have been collected in Sardinia over the course of several mineral prospecting campaigns. The sets of elements determined in each campaign varied, although analyses for most of the ore-related metals were normally performed. On this basis, the distribution of gold was studied because, in the set of metals known in the metallogeny of Sardinia, this metal was the last to prove economically recoverable. For this study, the territory of the whole island was subdivided into 110 districts and 26 sectors. This subdivision takes into account both the overall geological–lithological characteristics of each district and the total number of samples collected inside its limits. The results show that the metamorphic-dominated areas display a number of samples containing more than 20 ppb Au. This number is much higher than that observed in the granitic areas, not only as an absolute value, but also in relative frequency, which is more than twice that in the granitic areas. These high Au values are clearly clustered and related to ore-bearing structures.