Quebradona Project is owned and operated by Minera de Cobre Quebradona S.A.S. B.I.C., a company registered in Colombia. This entity is an indirect wholly-owned subsidiary of AngloGold Ashanti plc.
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Summary:
Geology
The geology of Nuevo Chaquiro consists of a volcanoclastic sequence of Miocene age (ash, tuffs, agglomerates and andesites) intruded by small dykes of diorite and quartz diorite which are also of Miocene age. The host rocks are intruded by different pulses of mainly medium to fine-grained quartz diorites. The majority of the intrusives do not reach surface and remain as a blind deposit despite erosion acting for a significant period. These intrusive rocks are categorised as pre-mineral, early, intra-mineral and late, according to cross-cutting interrelationships, spatial occurrence and copper-gold values. The alteration develops a well-zoned porphyry type system with alteration reflecting different temperatures from propylitic, sericitic, chloritic-sericitic, potassic to calcic-potassic assemblages. Higher-grade copper-gold mineralisation is associated with a well-developed quartz vein stockwork in the cupola zone of early quartz diorite which persists over a vertical interval of 500m.
Deposit type
Nuevo Chaquiro is a typical porphyry copper deposit with large tonnes and low-grade, with gold, molybdenum, and silver by-products. The structural setting facilitated the rise of intrusive bodies through the volcaniclastic sequence of the Combia Formation.
Mineralisation style
Five main targets have been identified in the exploration work, namely Nuevo Chaquiro, Aurora, Tenedor, Isabela, and La Sola. Nuevo Chaquiro is the most advanced and the sole mineral deposit considered in the feasibility study and licensing process. Nuevo Chaquiro, a significant copper-gold porphyry-style mineralised system, is one of three known porphyry centres on the property and has been the focus of exploration activities since the beginning of 2011 with more than 75km of drilling.
The Nuevo Chaquiro deposit consists of Miocene-aged diorite, quartz diorite dykes and thin vertical stocks intruding a thick succession of andesitic tuffs and volcaniclastic rocks of the Miocene age (6 to 10Ma) belonging to the Combia Formation. The Combia Formation fills a large pull-apart basin within the prospective middle Cauca Belt of central Colombia. Depth to mineralisation from the surface is around 150 to 400m from northeast to southwest. Typical copper porphyry alteration zonation is evident with a high temperature, potassium silicate central zone (biotite, magnetite, chalcopyrite and molybdenite), which trends into an overlying sericitic alteration zone (muscovite, chlorite, quartz, pyrite, tourmaline) surrounded by more distal propylitic alteration (chlorite, epidote, illite, carbonate). There is an inner core of calcic-potassic alteration featuring biotite, actinolite, epidote, and anhydrite with lesser copper, gold, and molybdenum values.
Mineralisation characteristics
An early dyke is located in the eastern part of the deposit and is the main supplier of the heat and hydrothermal fluids that caused the mineralising event. In the central area, abundant intra-mineral diorite and quartz diorites are found, which develop a classic ore shell of lower-grade mineralisation associated with these intrusions. Higher-grade copper-gold mineralisation is associated with a well-developed quartz vein stockwork in the cupola zone. The majority of the intrusive rocks do not outcrop. The mineralised zone is characterised by a fine stockwork with disseminations and veinlets of quartz, magnetite, pyrite, chalcopyrite and molybdenite.
Traces of bornite and cubanite have been locally observed in amounts less than 0.1% volume. Other sulphides include pyrite and pyrrhotite in specific areas. Gold and silver correlate well with copper, with gold grains dominantly occurring on the margins of sulphide grains within chalcopyrite.