The Manhulayan tenement comprises under-explored porphyry copper-gold and epithermal gold projects located near the intersection of two interpreted regional structures associated with strike-slip deformation along the Philippine Fault.
The key area of interest, the Costan Cu-Au porphyry prospect, comprises multiphase diorite intrusions hosted within propylitized andesitic volcanics. Low- and high-sulphidation epithermal gold mineralization (Monte de Oro prospect) and mesothermal gold-basemetal veins flank and partially overlap the Costan porphyry.
The host Costan Porphyry comprises a moderate, pervasive to selective potassic alteration zone with interdigitating but localized strong pervasive potassic and SCC (sericite-clay-chlorite) overprinting. A later stage of quartz-sericite-pyrite-calcite veining appears to carry much of the gold with attendant base metal mineralization.
The Manhulayan Intrusive complex has a strong aeromagnetic anomaly measuring 0.8km x 2.5km and coincident Cu and Au soil geochemistry. Locally, chalcopyrite-bearing veinlets crop out. A potassium geophysical anomaly coincides with the broad argillic blanket at the Monte de Oro prospect, possibly related to high level exposure of younger, concealed porphyry mineralization.
Deeper-level epithermal gold-basemetal veins impinge upon, and form a halo to the Costan porphyry stock. Many of these gold-basemetal veins have been extensively mined by local miners. In addition, higher-level epithermal gold mineralization (Monte de Oro prospect) occurs on the eastern margin of the Costan porphyry.
Four (4) shallow diamond drill holes (total 801.90 meters) targeted the outcropping Costan stockwork zone and coincident magnetic and radiometric anomalies. These holes represent a limited test of a small part of the Costan porphyry. Drill holes MDDH-1 and MDDH-2 averaged 185m @ 3370 ppm (0.34%) Cu + 0.16 ppm Au and 300m @ 3264 ppm (0.33%) Cu + 0.15 ppm Au, respectively. These holes intersected discontinuous mineralized zones in predominantly potassic-altered microdiorite. Intercepts include:
MDDH-1
• 26.2 m @ 3480 ppm (0.35%) Cu + 0.17 ppm Au, from 105.00 – 131.20 m
• 38 m @ 4026 ppm (0.40%) Cu + 0.125 ppm Au, from 147.00 to end of hole at 185.00. This zone is associated with moderate to strong veining and fracture-fill.
MDDH-2
• 15 m @ 5042 ppm (0.50%) Cu + 0.144 ppm Au, from 30.00 to 45.00 m
• 21 m @ 5242 ppm (0.52%) Cu + 0.20 ppm Au, from 75.00 to 96.00 m
• 15.80 m @ 5567 ppm (0.56%) Cu + 0.15 ppm Au, from 111.00 to 126.80 m
Costan shares similarities with other porphyry systems in the Philippines such as an outer halo of gold-rich base-metal veins. One of the larger veins can be seen in the old Manhulayan workings.
Scout drilling of the Monte de Oro epithermal gold prospect on the eastern flank of the Costan Porphyry is highly recommended to test the extent of higher-level epithermal gold mineralization and the potential for buried porphyry mineralization under an argillic-altered, broad airborne potassium anomaly and coincident high resistivity zone.
