GeoPeP 2011/2012

All locations are located in the North-east and East of Puquio. They are known targets of former mining exploration, as confirmed by national geological service of Peru, the Ingemmet.

Carhuarazo (CCAR) Lomada Atansa (ATAN) Cerro Chavina (CHAV) Cerro Orconcchocha (ORCO)

Cerro Orconcchocha (ORCO), around 14.59400 S and 73.94630 W

Map from the Cerro Orconcchocha Area

This location 20 km east of Puquio is represented by a ridge between two lakes. The vegetation is sparse. The outcrop represents an andesitic shield lava in the hanging wall of a sandstone whereas the andesite is thought to be Miocene in age. The andesitic rocks show variable degree of alteration, mostly silification and Fe-enrichment.
Fine-grained granular samples were taken from scree in alteration zones in order to cover different degrees of alteration. In addition, three rock samples were systemically collected to study a progressive trend of silification (ORCO-11-01-1, ORCO-11-01-2 and ORCO-11-01-3).

Cerro Chavina (CHAV), around 14.72023 S and 73.74522 W

Map from the Cerro Chavina Area

The investigation area is located 40 km east of Puquio. The location is crosscut by a U-form shaped valley, associated with glaciogenic deposits, e.g. a colluvium of fine-grained granulate.
The investigated inclination is composed of a hydrothermal altered andesite. A rhyodacitic to rhyolitic breccia crops out in the hangingwall of the ridge (see fig.1). The breccia is usually strongly weathered, mostly porous but can occur sometimes as a massive lava flow. The breccia shows a variety of alteration degrees, in particular high-temperature alteration and silification.

Fig.1: Picture from Cerro Chavina showing the Path of the Traverse

In order to observe changes in alteration type and intensity, a sample profile of fine-grained granular scree sediments was collected along the ridge (Fig.1).

Lomada Atansa (ATAN), around 14.57907 S and 73.85634 W

Map from the Lomada Atansa Area

This field site 30 km off Puquio and 10 km east of Cerro Orconcchocha is affected by glaciogenic processes similar to Cerro Chavina. Fine-grained clastic sediments can be found, sometimes associated with glacial mills.
The lithology is characterized by a weathered and altered grey ignimbrite which is crosscut by swarms of faults, striking in E-W direction. Intense clay-mineral alteration can be observed along the fault lines where the rock is crushed to a fine-grained mixture. A minimal thickness of 170 m is assumed for the ignimbrite that is superimposed by an andesitic lava-shield.
Samples of fine-grained granular scree sediments were taken with respect to variable alteration degrees of the ignimbrite, as well as the fault zones were sampled.

Carhuarazo (CCAR), around 14.32905 S and 73.77077 W

Map from the Carhuarazo Area

Located 56 km north-east of Puquio the volcanic structure of Carhuarazo is accessible by a trail above the village Chipao. The morphology is characterised by glacial valleys originated in a center above the sampled area. Meteoric water precipitates across the inclinations and dewatering takes place towards the glacial valley resulting in a water-rich area with distinct vegetation. Anthropogenic features indicate that Carhuarazo once was mined for gold by the Spanish conquerors. Moreover, it is a target of recent exploration.
The valley flanks are composed of rhyodacitic to andesitic lithologies in different types and degrees of alteration and weathering. Andesite might occur as a breccia. Hydrothermal alteration associated with Fe-hydroxides is a common feature. Opposing in-situ deposition, most material exists in form of fans made up of displaced brecciated rocks and associated fine grained granular scree sediments. Related to the water enrichment, massive Fe-hydroxide precipitation results in the formation of thick Fe-mineral enriched crusts.
Samples were collected primarily from the alterated fine scree fraction and in addition from the Fe-hydroxide crusts (CCAR-11-13 and CCAR-11-14).

© Christian Hansen, Andres Höweling, Kai Nitzsche, Tammo Ohlendorf 2012