The Crucero Project lies within the well established orogenic gold belt of South America. At the A-1 anomaly, the structurally-controlled mineralized zone appears to be directly associated with axial-plane deformation of a broad scale, north-plunging anticlinal sequence of carbonaceous slates and metasiltstones. Gold mineralization has a strong As-Sb affiliation. Gold appears to occur as saddle reefs (Windh, 1995; Schaubs et al., 2002) in very fine to micro-scale, sulfide-rich rhythmic bands or laminations, sulfide-rich veinlets with minor quartz and quartz veinlets and veins with polymetallic sulfides, rich in Sb. Stibnite also occurs as platings on fractures within the slates. Pyrite/pyrrhotite may also be found (locally), very finely disseminated in the host rocks.
The sulfide-rich bands and veinlets consist of pyrite, pyrrhotite, arsenopyrite, ± stibnite, ± chalcopyrite and gold. The polymetallic quartz veinlets and veins consist of pyrite, arsenopyrite, ± pyrrhotite, ± chalcopyrite, ± galena, stibnite and gold. Gold occurs in the free state and is closely associated with arsenopyrite. Gold may occur as inclusions, along fractures within arsenopyrite or as surficial attachments, as is the case in the Pataz district.
The region lies within the Cordillera de Carabaya (Clark et al., 1990). The northern part is underlain by the Coasa pluton of the Carabaya batholith. In the southern part, a sequence of carbonaceous shales and siltstones of the Siluro-Devonian Ananea Group is overlain to the west by quartz arenites of the Carboniferous Ambo Group. This sedimentary package is flanked by monzogranitic plutons; on the eastern side by the Limbani pluton and on the western side by the Aricoma pluton. The plutons were emplaced during the Late Triassic (ca. 225 Ma), (Kontak et al., 1990). The aforementioned lithologies lie, in part, within the Zongo-San Gabán tectono-thermal zone (ZSGZ: after Farrar et al., 1988, and Kontak et al., 1990d) in Clark et al. (1990).
The region was subjected to brittle-ductile deformation of east-west compression, and associated lower greenschist facies metamorphism during the Eo-Hercynian orogen. Haeberlin et al. (2004) suggest that the gold mineralization in the Pataz district took place 20 to 40 m.y. after the regional Eo-Hercynian orogen and postdated the 330 to 327 Ma calc-alkaline plutonism. The gold mineralization seems to correlate in time with a sedimentary hiatus, which fits with the general emergence that affected most of Peru during the Early Pennsylvanian. Haeberlin et al. (2004) further suggest that crustal thickening related to the Eo-Hercynian orogen and its abundant plutonism may have been the cause of the tectonic uplift and also may have triggered the thermal anomaly that provoked the release of large amounts of base metal- and gold-bearing fluids.
In the A-1 anomalous zone, carbonaceous shales and siltstones of the Siluro-Devonian Ananea Group are the host lithologies for the developing orogenic gold deposit. These rocks were demonstrably deformed during the Eo-Hercynian orogen. The resultant north-west trending structural zone with broad scale folding and attendant faulting is part of the greater Eastern Andean Cordillera belt that transects Peru, Bolivia and northern Argentina (Haeberlin et al., 2004). The prominent north-west trending ridges are moderately to highly silicified and chloritized in and adjacent to zones of gold mineralization. Just west of the currently defined mineralized zone, quartz-rich sandstones of the Carboniferous Ambo Group appear to be in reverse fault contact with the carbonaceous slates and metasiltstones.
Clark, A., Farrar, E., Kontak, D., and Langridge, R., 1990, Geologic and geochronologic constraints on the metallogenic evolution of the Andes of southeastern Peru: Economic Geology, v. 85, p. 1520-1583.
Haeberlin, Y., Moritz, R., and Fontboté, L., 2004, Carboniferous orogenic gold deposits at Pataz, Eastern Andean Cordillera, Peru: Geological and structural framework, paragenesis, alteration and 40Ar/39Ar geochronology: Economic Geology, v. 99, p.73-112.
Kontak, D., Clark, A., Farrar, E., Archibald, D., and Baadsgaard, H., 1990, Late Paleozoic-early Mesozoic magmatism in the Cordillera de Carabaya, Puno, southeastern Peru: Geochronology and petrochemistry: Journal of South American Earth Sciences, v. 3, issue 4, p. 213-230.
Robert, F., Brommecker, R., Bourne, B. T., Dobak, P. J., McEwan, C. J., Rowe, R.R., and Zhou, X., 2007, Models and Exploration Methods for Major Gold Deposit Types: in "Proceedings of Exploration 07: Fifth Decennial International Conference on Mineral Exploration", edited by B. Milkereit, 2007, p. 691-711.
Schaubs, P., and Wilson, C., 2002, The relative roles of folding and faulting in controlling gold mineralization along the Deborah Anticline, Bendigo, Victoria, Australia: Economic Geology, v. 97, p. 351-370.
Windh, J., 1995, Saddle reef and related gold mineralization, Hill End Gold Field, Australia: Evolution of an auriferous vein system during progressive deformation: Economic Geology, v.90, p. 1764-1775.