LITHOCAPS, ± AU-CU AND/OR ADJACENT EPITHERMAL VEINS, AND TRANSITION TO PORPHYRY CU-(AU) DEPOSITS: EXPLORATION GUIDES-JEFFREY W. HEDENQUIST EĞİTİMİ

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Lithocaps are permeablelithologic horizons that are altered to residual quartz with zoned halos ofquartz-alunite and aluminosilicate minerals; they are formed by acidiccondensates of magmatic volatiles derived from underlying intrusions. Lithocapalteration forms near the surface at the same time as potassic alteration ofunderlying porphyry deposits, due to the linked vapor and hypersaline liquid,respectively. Lithocaps are barren in metals on formation, but some aresubsequently mineralized with Cu (as high sulfidation-state sulfides, such asenargite) and Au. Epithermal veins may form on the margin of lithocaps, whetheror not the lithocap is mineralized. Several mineralized lithocaps areassociated with deeper porphyry Cu-Au deposits, including Lepanto and FarSoutheast, Philippines (1 Mt Cu, 105 t Au and 5 Mt Cu, 600 t Au, respectively),Bor and Borska Reka in Serbia (6.7 Mt Cu, 312 t Au and 3.7 Mt Cu, 142 t Au),and Tujuh Bukit and Tumpangpitu, Indonesia (65 t Au, oxidized, and 8.6 Mt Cu,855 t Au). Smaller examples of lithocaps related to porphyry deposits arepresent in the Biga region of Turkey. At Onto, Indonesia, the highsulfidation-state sulfides of the lithocap overprint earlier formed porphyrystockwork veins (15.4 Mt Cu, 848 t Au), although the upper ~300 m of thelithocap is essentially barren. The recently discovered high-grade overprint ofhigh sulfidation-state minerals on stockwork of the Filo del Sol porphyrydeposit (13 Mt Cu, 960 t Au, M+I), on the border of Argentina and Chile, sharesmineralogical similarities with Onto. Barren lithocaps can be underlain byporphyry deposits of the same age, including those at depth in the Escondidadistrict, Chile, and the Cocañez lithocap supradjacent to the Perol deposit,Peru. The Guinaoang quartz-alunite lithocap, 5 km from Lepanto, is a barrenzone over a deeper porphyry deposit, and likewise, the lithocap that outcropsabove the Rosia Poieni porphyry deposit, Romania, contains

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