1. Mobility of gold during metamorphism of the Dalradian in Scotland
- Abstract
Mobility of Au and related metals during metamorphism has been suggested to be the source of metals enriched in orogenic Au deposits. This study investigates the mobility of Au, As, and Sb during metamorphism of the Dalradian metasedimentary rocks of Scotland. The metamorphic processes in the Dalradian of Scotland are extremely well studied, and the terrane is an ideal area to investigate mobility of these metals. Our results show that of the 25 major and trace elements analysed, only Au, As, Sb, S and volatile contents as shown by loss on ignition (LOI) values show systematic variation with the metamorphic grade of the samples. Average Au concentrations decrease from 1.1 +/- 0.55 ppb and 0.72 +/- 0.34 ppb in chlorite and biotite zone rocks down to 0.4 +/- 0.22 ppb and 034 +/- 0.13 ppb in kyanite and sillimanite zone rocks. Average As concentrations decrease from 4.8 ppm (range 0.5 to 17.8 ppm) and 1.96 +/- 1.9 ppm in chlorite and biotite zone rocks down to 0.24 +/- 0.15 ppm and 0.2 +/- 0.12 ppm in kyanite and sillimanite zone rocks. Average Sb concentrations decrease from 0.18 +/- 0.15 ppm and 0.11 +/- 0.10 ppm in chlorite and biotite zone rocks down to 0.04 +/- 0.02 ppm in both kyanite and sillimanite zone rocks. Sulphur and LOI concentrations also show significant decreases. Mass balance calculations indicate that compared to chlorite and biotite zone samples, sillimanite zone samples have an average mass loss of 62 +/- 14%, 94 +/- 4% and 74 +/- 14% for Au, As, and Sb respectively. Every 1 km(3) of chlorite-biotite zone mixed psammitic-pelitic protolith rock that is metamorphosed to sillimanite zone conditions would release 1.5 t Au, 8613 t As, 270 t Sb, and 1.02 Mt S. The mobility of these elements is strongly controlled by the paragenesis of sulphide minerals. Pyrite, sphalerite, galena and cobaltite (as well as gersdorffite) decrease in abundance with increasing metamorphic grade in the Dalradian metasedimentary rocks. A critical aspect of the sulphide paragen
- Published
- 2015
- Full Text
- View/download PDF