Using melt inclusions to understand magmatic-hydrothermal evolution in epithermal-porphyry copper environment: some examples from mining areas of Peru and Romania

摘要

Melt inclusions trapped in igneous phenocrysts were used to characterise calc-alkaline magmas associated with epithermal deposits in the Shila district, Peru, and the Valea Morii porphyry-copper deposit, Romania. Cl contents in remelted inclusions from quartz phenocrysts of Shila district are up to 1.9~*10~3 ppm and the melts in some inclusions are enriched in Cu (up to 1.6~*10~3 ppm). X-ray map of one inclusion (EMPA) reveal a strong enrichment in Cl in the vapor bubble. These observations clearly show that the volatile phase of magmas might be the precursors to ore-forming epithermal solutions. For the porphyry-copper environment (Valea Morii, Romania), a comparative study of mineralised intrusions vs. barren intrusions reveals parameters which may influence the magmatic-hydrothermal connection. The present results emphasize the importance of the chemistry of residual melts (trapped in magmatic inclusions) rather than bulk magma compositions (derived from whole rock analysis) in determining the metal concentration in released magmatic fluid.