The porphyry copper-gold deposit Quicay II, has a stratigraphic sequence that ranges from the Precambrian to Quaternary periods in an intermittent but relatively constant manner, with several sedimentary hiatus periods, that passes from the continental territory in the Paleozoic to the marine in the Mesozoic and finally to the volcanic continental in the Cenozoic. In this sequence, the Excélsior, Pucará and Goyllarisquizga groups are found. Equally, the Pocobamba formation, Calera formation and quaternary deposit can be found.

 

Likewise, the area found in Quicay II can be defined as a plateau of approximately 30 x 12 km fully covered by moraines. In this same area, some volcanic outcropping remains exist, such as Quicay, Pacoyán, Raco and Malarín.

 

Quicay II is formed by volcanic structures which probably started with a pyroclastic phase, followed by the settlement of andesitic, dacitic and tuff lava, and in the final stages by the intrusion of diorite and monzonite quartz. Structurally, Quicay II is dominated by the nearby presence of big regional dextral reverse and Andean strike faults, with a SSE-NNW direction within the area of the project. Furthermore, Quicay is the main and most representative ore deposit of the Quicay–Pacoyán belt with Au–Ag high sulphuration veins and epithermal bodies.

 

The Quicay II deposit is placed on volcanic rocks with dacite-andesite composition with advanced argillic alteration evidences on the higher levels, grading to an intrusive body of porphyritic dacitic-andesite porphyry composition with argillic, phyllic and potassic alteration to a bigger depth. Regarding disseminated mineralization, 50% of it is present in the intrusive rocks and the other 50% is controlled by the hydrothermal stage of quartz-sulphide stockwork veinlets.

 

The zonal sequence of the alterations variations and mineralization in depth, are summarized as follows:

 

• Argillic alteration occurs on superior levels and towards the external section. It consists of kaolin and pyrite and some boreholes have intercepted remains of advanced argillic alteration (quartz-kaolin-alunite).

 

• Phyllic alteration occurs on superior levels and towards the external section. It consists of kaolin and pyrite and some boreholes have intercepted remains of advanced argillic alteration (quartz-kaolin-alunite).

 

• Phyllic alteration is found deeper and is especially related to stockwork areas and to rich concentrations of Cu-Au ore. Alteration consists of quartz-sericite-pyrite.

 

• Potassic alteration was intercepted at some boreholes, at 700-750 metres approximately. It consists of secondary biotite, magnetite and variable quantities of potassic feldspar.

 

• Different types of rocks and mineralization of sulphides were intercepted after finishing the moraine zone and lacustrine material with a variable thickness of 100-12 meters.

 

• Oxidation area is absent in most of the boreholes. Generally, mineralization starts with a supergenic enriching area with variable thickness of 0-70 metres. It consists of chalcocite and pyrite, then there is a transition area with covelline, chalcocite, chalcopyrite, enargite, molybdenite and pyrite mineralization related to the phyllic alteration up to an approximate depth of 500 metres. The primary mineralization is present at a bigger depth, this consists of chalcopyrite, bornite, molybdenite and pyrite related to phyllic and potassic alteration.