Abstract

The Aguablanca Ni-Cu ore deposit is hosted by subvertical magmatic breccia bodies in which fragments of pyroxenite are cemented by sulfides. It is located within the Aguablanca Stock, which includes diorite, gabbro, norite and gabbronorite. Re-Os isotope data of magmatic pyrrhotite, chalcopyrite, and pentlandite and hydrothermal pyrite show that the Os has a mixed origin, derived from a juvenile mantle source and a crustal source. The more likely contaminant of the primitive melt is the late Neoproterozoic to early Cambrian sequence that extensively crops out in the area. Data from the disseminated ore are aligned along a reference line yielding 383 ± 59 Ma (MSWD = 3.0; 187Os/188Osi = 0.17 ± 0.01). This age is similar to previous 40Ar/39Ar and U-Pb data of the host rocks (ca. 340 Ma) and confirms that both the host rocks and the mineralization are Variscan in age. These results also show that both the magmatic and hydrothermal processes took place in a short time span, with the hydrothermal pyrite being isotopically similar to the magmatic sulfides. However, some Re-Os results from massive sulfides are discordant to the observed trend and are attributed to a late alteration of the Re-Os system during late- to post-Variscan hydrothermal and supergene alteration. This alteration produced a variable and unsystematic variation of both Re and Os in the sulfides. Copyright © 2008 by Bellwether Publishing, Ltd. All rights reserved.