The Jasperoide project area is underlain primarily by marine limestone of the Middle Cretaceous Ferrobamba Formation and intrusive rocks of probable Eocene-Oligocene age. The limestone - intrusive contact is irregular, north and west of the main skarn deposit, the Ferrobamba occurs as large roof pendants and embayments in granodiorite. Within the deposit, mineralized skarn bodies, mantos, and dioritic dikes dip westerly 10 to 30 degrees. The lower portion of the Ferrobamba Limestone and underlying Mara Formation, the principle host rocks at Las Bambas, have not been tested by drilling at Jasperoide.
The intrusive suite includes the main granodiorite batholith and 2-3 phases of diorite, diorite porphyry, and quartz monzonite. The main granodiorite mass occurs adjacent to and intrudes the limestone sequence and is extensively argillized in surface exposures. This diorite suite is genetically associated with skarn formation and Cu-Au mineralization. Near intrusive contacts, the diorite is highly altered to massive and vein-controlled endoskarn assemblages.
Jasperoide represents a classic, calcic exoskarn deposit that developed in the upper to middle part of the Ferrobamba Limestone. Copper and gold mineralization is associated with prograde garnet-magnetite-limonite skarn, diopside-garnet skarn, and massive magnetite lodes and skarn bodies. Chalcopyrite, bornite, and pyrrhotite are the primary ore minerals associated with prograde garnet (andradite+grossular) skarn. Covellite, digenite, and chalcocite are also present and may represent supergene enrichment or may be associated with hydrous retrograde alteration. Skarn mineralization at surface and in drill core is strongly oxidized with significant malachite, brochantite, azurite and chrysocolla. Late, quartz-calcite-specularite veins, hydrothermal breccias, and jasperoid replacement of limestone likely represents a younger, gold-rich epithermal event superimposed on earlier skarn assemblages.
There are three principal fault patterns at Jasperoide, mainly sub-vertical faults that generate a sequence of down-dropped (graben) and raised (horst) blocks.
1. A pre-mineral north-south system that influenced the N-S elongated emplacement of the intrusive rock,
2. Northeast-southwest oriented faults that cross-cut the north-south fault set that appears to be syn-mineral, and
3. An east-west striking fault orientation that has minor offset and post-dates the Cu-Au mineralizing event.
The faults are apparently deep-seated and influence the geometry and relative vertical position of the individual fault blocks.