Fluid evolution in the Cu-Au deposit related to the Carles granodiorite (Asturias)

The Carles Cu-Au deposit, in the outermost zone of the Hercynian Iberian Massif, is associated with a small intrusive granodiorite of late Hercynian age (283 + or - 6 m.y.). Four different types of alteration characterize the deposit: a skarn developed in marbles, an amphibole-arsenopyrite replacement of the marbles and earlier skarn, a K-feldspar alteration mainly in the granodiorite and a greisen-type alteration also in the granodiorite. The exoskarn and an endoskarn alteration were the first alterations in a high-T episode (720-500 degrees C), whereas the other three occurred together with the ore minerals in a lower T stage (500-300 degrees C). Ore mineralogy in the skarn veins and K-feldspar alteration consists of Cu sulphides and significant amounts of Au; in the greisen and amphibole-arsenopyrite alterations the dominant sulphides are arsenopyrite, loellingite and pyrite (gold has not been detected). Fluid inclusions in garnets from the exoskarn and in quartz from skarn veins and altered K-feldspar are highly saline (up to 48 wt.% NaCl eq.), with small quantities of CO (sub 2) ; those in quartz from greisen and amphibolite-arsenopyrite alteration show low salinity (<<<$I> 6 wt.% NaCl eq.), significant CO (sub 2) (XCO (sub 2) approximately 0.15-0.03) and small amounts of CH (sub 4) , N (sub 2) and H (sub 2) S. It is considered that Au and Cu were fractionated preferentially into the high-salinity fluid.