karst investigation report

KARST INVESTIGATION OF THE TAILINGS SITE OPTIONS AT PUNRRE AND QUEBRADA HIERBA BUENA

EL GALENO PROJECTSOROCHUCO, CELENDIN, CAJAMARCA

Prepared for:

NORTHERN PERU COPPER CORPORATIONClient AddressClient Address

City, State (spell out) Zip+1-area code-prefix-number

Prepared by:

VECTOR PERU SACJorge Vanderghen 234

Miraflores, Lima 18, Perú511-441-2300

J06.82.03.00May, 2006

Recycled Paper

Karst Investigation of the Tailings Site Options May 2006El Galeno Project, Cajamarca J06.82.03.00Northern Peru Copper Corporation

TABLE OF CONTENTS

1.0 OBJECTIVE............................................................................................2

2.0 LOCATION AND ACCESS.........................................................2

3.0 WEATHER.............................................................................2

4.0 GENERAL GEOLOGY...............................................................2

5.0 KARSTIC GEODYNAMICS........................................................35.1 Punrre Area (Option 1)..................................................................35.2 Hierba Buena Area (Option 2).......................................................4

6.0 CONCLUSIONS......................................................................5

7.0 RECOMmENDAtIONS............................................................................6

LIST OF FIGURES

Figure 1 Options for Tailings Site

Vector Perú S.A.C. Calle Jorge Vanderghen 234, Miraflores Lima 18, Perú (51-1) 441-2300-i-

Recycled Paper


1.0 OBJECTIVE

The objective of this reconnaissance was to determine the geological and

hydrogeological conditions of two tailings site options, Punrre and Hierba

Buena, respectively, for El Galeno project, Cajamarca. These areas have

carbonated rocks prone to develop karstic process.

Field work consisted on:

Surface geological reconaissance,

Description of the karstic process,

Location of sinkholes, dolines, caverns and water surges, and

Surface runoff and underground infiltration reconnaissance.

2.0 LOCATION AND ACCESS

The project area is located in Cajamarca, southeast of Sorochuco, province

of Celendín, at approximately 4,000 masl. Access to the project area is

through a gravel road and sidewalks to specific areas.

3.0 WEATHER

The project area is foggy and rainy during summer, whereas the winter is

dry and cold.

4.0 GENERAL GEOLOGY

Lithology of the potential tailings site areas is mainly composed by

sequences of carbonated rocks (limestone), interlayered with clayey-silty

layers, prone to develop karstic process. These rocks belong to the

Chulec-Pariatambo Formation in the Punrre area, and to the Chulec

Formation in the Hierba Buena area. These formations are from the early

to late Cretaceous. At the adjacent and peripherical areas, Quartzites of

the Goyllarisquizga group from early Cretaceous, and volcanic rocks of the

Calipuy group from the Cenozoic predominate.

Vector Perú S.A.C. Calle Jorge Vanderghen 234, Miraflores Lima 18, Perú (51-1) 441-2300-2-

Recycled Paper


The region is affected by a structural system of regional reverse faulting

and transversal normal faulting, perpendicular to the over-slipping.

5.0 KARSTIC GEODYNAMICS

The tailings site areas have been evaluated considering hydrogeological

and structural conditions, as well as karstic development. The Punrre area

is named Option 1 and the Hierba Buena area is named Option 2. Figure 1

shows the location of these options.

The karstic process is caused by the presence of carbonated rocks

combined with a rainy regime, water acidity and structural factors. These

factors produce karstic aquifers and cavern formation or speleogenesis.

5.1 Punrre Area (Option 1)

In this area the karstic process has been limited by the structural

alignments composed by a longitudinal reverse faulting system and

transversal normal faulting, fracturing and jointing, which have formed

karstic hydrogeological systems connected through underground networks

and sinkholes. There are also collapsed dolines, which partially

contributes to the storage of rain water, which then infiltrates to the

ground through the fractures and joints of limestone rocks.

In the western side of Punrre area, groundwater flow predominates and

the karstic forms are more evolved and developed than in the central and

eastern areas. The karstic systems are considered in its early stage. They

end near the Punrre village, in the Cueva del Gato cavern.

The water chemistry in the western header, where the ponds and sinkhole

appear, indicates pH values between 4 and 5, whereas in the distal zone

these values are between 7 and 8. This indicates the water acidity

decreases at the distal zone or surge area of Cueva del Gato, due to

chemical disolution.


Recycled Paper


Cueva del Gato Cavern

This cavern constitutes a collector and source of important groundwater

flow, which is used for domestic and hydroelectric use by the Punrre

village and other small villages. This cavern has a length of about 250 m.

The following photograph illustrates this cavern.

Photo 1 Entrance of Cueva del Gato cavern at Punrre

5.2 Hierba Buena Area (Option 2)

Based on the general field reconnaissance the Hierba Buena area is

considered a better area for foundation of the tailings deposit than the

Punrre area. It is constituted by sandy and clayey-silty limestone

interlayered with clayey-silty layers, which probably have conditioned the

development of karstic structures, existing only shallow erosion traces.

The layers of clayey-silty work as an impermeable layer, avoiding the

development of groundwater flow. In this area drainage is superficial and

continuous. The following photo shows the Hierba Buena area and the

tailings dyke zone.


Recycled Paper


Foto 5 Hierba Buena tailings dam site.

6.0 CONCLUSIONS

The following conclusions are obtained from the karstic investigation for

the tailings site options for El Galeno project:

The most significant karstic process occurs at the western side of Punrre

or Option 1, with an alignment northwest-southeast.

Field observation of the superficial drainage at Punrre area indicates the

presence of small collapsed sinkholes, which capture water underground.

Then, this water surges downstream, confirming the existence of a young

underground karstic network, which is more developed at the western

side than the eastern side.

The Cueva del Gato cavern is an important collector and issuer of

groundwater from the underground karstic network at the western of

Option 1 area.

In the Hierba Buena quebrada the stratigraphy of impermeable clayey

limestone and layers of clayey-silty rocks do not allow the karstic process.


Recycled Paper


The main drainage in the Hierba Buena area is composed by superficial

and continuous runoff, indicating no significant karstic process.

The Hierba Buena area presents the most appropiate geological and

geotechnical conditions for foundation of the tailings dam, requiring

further detailed investigation.

The alternative of quebradas Chancas, Yanacocha and Río Grande is

considered less feasible for a tailings deposit, since it involves more

populated areas and extensive agricultural and cattle rising activities.

7.0 RECOMMENDATIONS

The following recommendations are given for further study of these areas:

To prepare a geological mapping of lithological facies and detailed

geotechnical mapping for the Hierba Buena area, for characterization of

the rock masses.

To prepare detailed stratigraphic cross sections for the Hierba Buena

area, for defining the continuity of the silty-calcareous facies and the

clayey-silty layers.

To investigate in detail the header and upstream slopes of the Hierba

Buena quebrada in order to locate or discard the presence of karstic

structures.

To collect microtectonics data in the study areas.

To conduct a detailed hydrogeology study in the involved areas of the

project.

To perform electric surveying at the karst areas.


karst investigation report

Documents