Fluid inclusions and quantitative model for gold precipitation in the Tiouit deposit (Anti-Atlas, Morocco)

Abstract

In the Tiouit gold deposit (Anti-Atlas, Morocco), a paragenetic study has revealed the existence mainly of two generations of gold, the earliest one was cogenetic with ferro-arseniferous stage I; the second generation (most important) is associated with the minerals of a cupro-zinciferous sulphide stage II. A microthermometric study of fluid inclusions demonstrates that the main part of the gold was introduced by an aqueous solution of relatively low salinity (1.7 m Nacl) and deposited at about 400 °C and 500 bars in microfractures crosscutting early sulphides. A calculated quantitative model for the fluid-mineral interaction demonstrates that a significant amount of gold (3 mg deposited from 1 kg of solution, i.e. 43% of total gold), transported as bisulphide complexes ( HAu ( HS ) 2 0 , AuHS 0 and Au ( HS ) 2 - ), can be deposited as a result of a decrease in both H 2S activity and oxygen fugacity produced by the alteration of pyrrhotite into pyrite.