Silicate-melt and fluid inclusions in rhyolitic dykes, Los Manantiales mining district, Argentina
Varela, Maria Eugenia
European Journal of Mineralogy Volume 6 Number 6 (1994), p. 837 - 854
published: Nov 30, 1994
manuscript accepted: Jun 1, 1994
manuscript received: Dec 17, 1992
ArtNo. ESP147050606010, Price: 29.00 €
Abstract The Angela mine is an epithermal polymetallic deposit located in the Los Manantiales mining district of Argentina, in a Kimmeridgian-Titonian volcanic complex. The epithermal veins may be genetically related to a late magmatic event, characterized by the emplacement of rhyolitic intrusions. Several types of glass inclusions as well as biphase and polyphase aqueous inclusions were studied in these rhyolitic dykes. Glass inclusions show initial melting at 700°C-800°C. Devitrification of silicate-melt inclusions can be attributed to fluid circulation; electron microprobe analyses indicate Na2O and K2O depletion and SiO2 enrichment. Solid phases in primary polyphase aqueous inclusions are most likely chlorides. Salinities, calculated from final daughter-mineral dissolution, range between 85 and 34 NaCl wt% eq. Considering the partition coefficient value for chlorine (KpCl-= 49) and pressure determination on type-A inclusions (446 bars), the possible fluid evolution began with hypersaline fluids exsolved in the late magmatic stage from the rhyolitic magma. Dilution of these fluids is suspected to have contributed directly to the formation of the ore.