Original paper

The volcanic copper deposits of Caprichosa, Antachajra, and Luiza in Central Peru - a case study on paragenesis and wall rock alteration

Thum, R.

Neues Jahrbuch für Mineralogie - Abhandlungen Band 144 Heft 2 (1982), p. 125 - 147

25 references

published: Aug 1, 1982

BibTeX file

ArtNo. ESP154014402001, Price: 29.00 €

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Abstract

The deposits of Caprichosa, Antachajra and Luiza are situated in the Central Andes of Peru, about 120 km E of Lima, 7 km SE of the mining town of Casapalca and at an altitude of 4800 to 5000 m. The geological setting is determined by a sequence of mainly volcanic rocks of Eocene to Miocene age. The three deposits are located within one and the same horizon of andesitic porphyries ("Carlos-Francisco Porphyry"). The ore appears in lenticular or irregular zones with widths up to 40 m and lengths up to 200 m. The main ore minerals are chalcopyrite, bornite and As-rich fahlore. Two types of ores can be distinguished: a disseminated and a massive (stringer, lenses) ore type. Between both types exist gradual transitions. Within and around the deposits, small ore bearing quartz-calcite veins are found which are younger than the other ore types and show different parageneses. The wall-rock in the area of the deposits is hydrothermally altered, and a zonation can be established (chloritization, carbonatization, silification and sulphidization). The different degrees of alteration are (mostly) related to typical rock colours in the field. Based on the paragenesis, the geometrical distribution patterns (in the field as well as on microscopical scale), and geochemical investigations, it is indicated that the three deposits formed by low grade hydrothermal processes connected with the volcanism of the Carlos-Francisco Formation. Compared to other well-known deposit types, these deposits seem to be similar to a "stockwork type" which is often found below the base of massive sulphides. We are probably dealing here with a deposit type intermediate between volcanogenic-exhalative (e.g. the Kuroko type) and subvolcanic (e.g. porphyry copper) sulphide deposits. There is no structural or textural or even mineralogical evidence that direct genetic connections exist between the neighbouring Casapalca vein deposit and the Caprichosa, Antachajra, and Luiza deposits. Only the small and younger veins in this area can be considered to belong to the Casapalca system.

Keywords

Copper sulfidehydrothermal depositore disseminationchalcopyritebornitetetrahedriteandesitic rockTertiaryhydrothermal wall-rock alterationzonationvem deposit (Casapalca system)Peru (CaprichosaAntachajraLuiza)