Mineral Paragenesis of the Lepanto Copper and Gold and the Victoria Gold Deposits, Mankayan Mineral District, Philippines

Abstract

: Mineral paragenesis of the alteration, ore and gangue minerals of the Lepanto epithermal copper‐gold deposit and the Victoria gold deposit, Mankayan Mineral District, Northern Luzon, Philippines, is discussed. The principal ore minerals of the Lepanto copper‐gold deposit are enargite and luzonite, with significant presence of tennantite‐tetrahedrite, chalcopyrite, sphalerite, galena, native gold/electrum and gold‐silver tellurides. Pervasive alteration zonations are commonly observed from silicification outward to advanced argillic then to propylitic zone. The ore mineralogy of the Lepanto copper‐gold deposit suggests high fS2 in the early stages of mineralization corresponding to the deposition of the enargite‐luzonite‐pyrite assemblage. Subsequent decrease in the fS2 formed the chalcopyrite‐tennantite‐pyrite assemblage. An increase in the fS2 of the fluids with the formation of the covellite‐digenite‐telluride assemblage caused the deposition of native gold/electrum and gold‐silver tellurides. The principal ore minerals of the Victoria gold deposit are sphalerite, galena, chalcopyrite, tetrahedrite and native gold/electrum. The alteration halos are relatively narrow and in an outward sequence from the ore, silica alteration grades to illitic‐argillic alteration, which in turn grades to propylitic alteration. The Victoria gold mineralization has undergone early stages of silica supersaturation leading to quartz deposition. Vigorous boiling increased the pH of the fluids that led to the deposition of sulfides and carbonates. The consequent decrease in H2S precipitated the gold. Gypsum and anhydrite mainly occur as overprints that cut the carbonate‐silica stages. The crosscutting and overprinting relationships of the Victoria quartz‐gold‐base metal veins on the Lepanto copper‐gold veins manifest the late introduction of near neutral pH hydrothermal fluids.

Zonation of Sulfate and Sulfide Minerals and Isotopic Composition in the Far Southeast Porphyry and Lepanto Epithermal Cu–Au Deposits, Philippines

“…These include the formation lifetime of many porphyry deposits (Arribas et al, 1995a), the relation of the potassic stage to the formation of the lithocap, as well as the high sulfidation-state mineralization of the latter by a subsequent, but still magmatic-dominant fluid, during the phyllic-stage overprint (Arribas et al, 1995a;Hedenquist et al, 1998), and the integral association of the intermediate-sulfidation Victoria veins with the porphyry system (Claveria, 2001;Chang et al, 2011).…”

“…3b). Stage 2b gold occurs in microfractures that cut enargite ± luzonite, accompanied by tetrahedrite, chalcopyrite and sphalerite plus telluride and selenide minerals (Gonzalez, 1956;Tejada, 1989;Claveria & Hedenquist, 1994;Claveria, 2001;Fig. 4d).…”

“…The Lepanto high-sulfidation Cu-Au deposit is elongate along the Lepanto fault, NW of the surface projection of the FSE porphyry deposit; the Victoria-Teresa intermediatesulfidation vein complex (Claveria, 2001) lies about 500-1000 m south of FSE (Fig. 1).…”

“…The ore minerals at Lepanto consist mainly of enargite deposited in fractures and breccias that post-date formation of the advanced argillic alteration ( Fig. 3; Hedenquist et al, 1998;Claveria, 2001); there is also luzonite and minor chalcopyrite plus various gold-and silver-bearing minerals. Alunite and aluminum phosphate-sulfate (APS) minerals of the alunite supergroup are characteristic of advanced argillic alteration (Meyer & Hemley, 1967;Hemley et al, 1969;Stoffregen & Alpers, 1987;Aoki, 1991), and their isotopic composition, including O, H and S, has been used to help constrain formation conditions (Rye et al, 1992;Arribas et al, 1995b;Deyell et al, 2005a, b).…”

Victoria Carbonate‐Base Metal Gold Deposit and Its Significance in the Mankayan Mineral District, Luzon, Philippines

“…The LCC also defines a mineral belt, along which the Mankayan and Baguio districts are disposed. Significant deposits include the FSE (Concepción and Cinco, 1989;Hedenquist et al, 1998;Imai, 2000) and Santo Tomas II (Philex) (Serafica and Baluda, 1977;Imai, 2001) porphyry copper-gold deposits, the Thanksgiving skarn-type zinc deposit (Callow, 1967), and epithermal gold deposits such as the Antamok and Acupan low-sulfidation deposits Sawkins et al, 1979;Cooke and Blooms, 1990) and the Lepanto highsulfidation deposit (Gonzalez, 1956;Garcia, 1991;Hedenquist et al, 1998;Imai, 1999;Claveria, 2001). These deposits are genetically associated with Western Luzon arc magmatism (Sillitoe and Gappe, 1984;Mitchell and Leach, 1991;Sajona and Maury, 1998;Imai, 2002).…”