GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 32-7
Presentation Time: 3:20 PM


SMITH, Quinn Eric, Geoscience and Discovery, MMG ltd, 390 Union Blvd, Suite 200, Lakewood, CO 80228,

Information on vein density, orientation, and paragenesis was collected during detailed pre-mining outcrop mapping and drill hole re-logging at the Ferrobamba Cu-Mo porphyry deposit in the Apurimac province, central Peru. Vein-focused Anaconda-style mapping was conducted at 1:5 scale, with 123 stations mapped on a 50cm by 50cm field grid. The distribution of vein density (n/cm) varies systematically with host rock and alteration intensity across the deposit, but is complicated by multiple overprinting intrusive events. High vein densities (n > 0.6 cm-1) occur in discreet zones within a broader north north-west corridor of moderate vein densities generally limited to the spatial extent of the Jahuapaylla stock and associated dikes. Little to no veining can be traced into the limestones of the Ferrobamba Formation, however considerable quartz veining is hosted in endoskarn and skarn zones within and around the Ccomerccacca and Jahuapaylla stocks. A significant change in dominant vein orientation occurs with the emplacement of the mineralizing Jahuapaylla stock and late monzodiorite dikes, indicating a change in the dominant stress regime associated with mineralization. Vein cross-cutting relationships indicate nine vein assemblages progressing from sugary quartz, to quartz-albite, dark micaceous and wispy biotite-sulfide veinlets, sodic-calcic actinolite-Na-feldspar, calc-potassic quartz-k-feldspar-actinolite-apatite, quartz-k-feldspar, quartz-bearing biotite, grey-banded and B veins, and finally banded carbonate-sulfosalt veins. Calc-potassic veins are often overprinted by and transition to skarn assemblages. Quartz-bearing biotite veins cut and offset calc-potassic veins, extend into skarn zones, and are associated with strong bornite-chalcopyrite-molybdenite mineralisation around the Jahuapaylla stock. Alteration zones from a potassic assemblage of dominantly secondary biotite within the Jahuapaylla stock, passing to argillic, sodic, and distal propylitic. Skarn alteration of the Ferrobamba limestone extends up to 100m outward from the Jahuapaylla stock, hosting high-grade mineralization. Vein density, paragenesis and alteration zoning indicate the Jahuapaylla stock was the source of the bulk of porphyry-style alteration and mineralization at Ferrobamba.