GEOLOGICAL SOCIETY OF THE PHILIPPINES

 

THE DISCOVERY OF THE LEPANTO VICTORIA GOLD DEPOSIT, MANKAYAN, BENGUET, PHILIPPINES

 

Ana Liza G. Cuison, Rene Juna R. Claveria and Benigno V. Andam
Lepanto Consolidated Mining Company

 

        The Victoria gold deposit lies within the LCMC property which also bounds the two (2) well known Cu-Au deposits, the Enargite epithermal copper (+gold) and the FSE porphyry copper (+gold) deposits. The shift of Lepanto from a predominantly copper mine to a gold mine was significant for the fast track development in mining and gold production. It took only a period of 18 months from the discovery to the production stage, which makes the Victoria deposit one of the fastest underground gold projects to be developed.

        Exploration diamond drilling both surface and underground were intensified during the early months of 1995, to define the mineralization in the Nayak Pacda gold belt south of the enargite copper zone. A surface hole intersected a 21.6-meter wide mineralized zone with an average of 3.7 g/t Au and a subsequent underground hole intersected eight (8) mineralized zones with grades ranging from 1.3 to 193 g/t Au, making them the discovery holes of the Victoria deposit.

        Preliminary estimate shows an ore resource of 4.9 Mt at 7.82 g/t Au, and a geological resource of 4.6 Mt at 6.47 g/t Au.

        The Victoria gold deposit is a low sulfidation quartz vein deposit hosted by dacite pyroclastics/porphyries and volcaniclastics. It is composed of 14 major ore zones with each zone consisting of several veins. Open space crustiform and banded structures are observed in the formation of both gangue and ore minerals. The dominant ore minerals are sphalerite, galena and chalcopyrite. Gold occurs either as free grain in quartz or in association with the other sulfides. The predominant gangue minerals are quartz, carbonates and gypsum. The alteration halos around veins are relatively narrow consisting of silicic, sericitic-argillic and propylitic zones. Initial fluid inclusion studies in quartz and sphalerite show temperatures of formation ranging from 108.9 to 227.8oC. Preliminary paragenetic studies show apparent 3 stages of mineralization: an early quartz (-gold) stage, a carbonate stage and a late gypsum stage. The abundance of base metals relatively decreases towards the gypsum stage.

        The gold deposit could have some genetic associations with the Enargite deposit and probably indirectly with the FSE porphyry system. It is relatively apparent that the Victoria quartz-gold-base metal veins could have occurred similarly as the quartz-gold roots overprinting the enargite mineralization. This overprinting signifies the waning stages of the entire hydrothermal system.

 
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