New tools for exploring lithocaps: example from the Mankayan intrusion-centered Cu-Au district, Philippines

The Lepanto high-sulfidation epithermal deposit is hosted in a lithocap that is genetically linked to the Far Southeast porphyry, with both deposits largely under cover. Several characteristics of the Lepanto lithocap were found in this study to change systematically with distance from the causative intrusion, although surface samples of the lithocap are mostly barren and do not define mineralogical or textural zonation patterns relative to the intrusive source. The alunite absorption peak at ~1480 nm in short-wavelength infra-red spectra shifts to higher wavelength positions in samples closer to the intrusive center. The alunite Pb content and Ag/Au ratio decrease towards the intrusive center, whereas Sr, La, Sr/Pb and La/Pb increase markedly. Whole-rock compositions, using only non-mineralized (Cu <0.1wt% and Au <0.1 ppm) and alunite-bearing samples, show that Pb, Hg, Ag, and Ag/Au decrease towards the intrusive center, and La/Pb and Sr/Pb ratios increase.