Geoscience Reference
In-Depth Information
14
Case Studies
Abstract
This chapter presents a few real-life examples of different types of Mineral Resource Es-
timation and Geostatistical studies. They are intended to illustrate some of the techniques
described in the topic, but are not exhaustive in scope or content.
14.1
The 2003 Cerro Colorado Resource
Model
Cerro Empexa Formation underlies most of the Cerro Colo-
rado region. Multiple phases of tonalite, granite and quartz
monzonite porphyry were emplaced into the volcanic rocks
in late Cretaceous and early Tertiary time. Copper miner-
alization is related to late-stage intrusives of tonalite and
quartz monzonite microbreccia. Andesites and intrusives are
covered by a locally thick sequence of Pliocene ignimbrites
and gravels of the Altos de Pica Formation.
Copper occurs in a series of sub-horizontal layers of su-
pergene oxide minerals and supergene sulfides. Mineral-
ization occurs in andesite and porphyry along an east-west
to northeast trend. Copper mineralization extends at least
2,000 m East-West and from 1,000 to 2,000 m North-South.
The orebody is covered by post-mineral gravels and ignim-
brites of the Altos de Pica Formation, except for some oxide
ore exposed in a nearby gully (Quebrada de Parca).
Mineralization is thickest in two distinct areas, forming
the West and East deposits. Mineralization in the West de-
posit is generally centered along the southern margin of an
east-west trending body of porphyry where elongate fingers
of microbreccia are developed in porphyry and andesite. The
East deposit is located along the southern flank of a north-
east-trending body of quartz monzonite microbreccia. The
deposit is centered in an area where abundant, small apophy-
ses of porphyry intrude andesitic tuffs and porphyritic flows.
The Cerro Colorado Mine is located at an elevation of
2,500 m, on the western slopes of the Andes in Northern Chile.
The mine is located about 120 km east of the city of Iquique
(Fig.
14.1
), on the western edge of the Domeyko Cordillera.
The Cerro Colorado mine is a bio-heap leach, solvent
extraction-electro winning (SX-EW) copper operation, has
been in production since 1994. It started up as a small open
pit operation, producing in the order of 20,000 t of cathode
copper. As of 2003, and after several expansions, the mine
was producing about 120,000 t of cathode copper per annum.
Originally operated by the Rio Algom mining company, later
became part of the assets transferred to the Billiton min-
ing company as part of its merger with Rio Algom, and in
2001 became part of the BHP-Billiton base metals group.
Figure
14.2
shows an aerial view as of 1999 of the mine op-
eration. The overall drill hole spacing at the time of prepar-
ing this resource model was a nominal 100 × 100 m, with
some areas infilled to 50 × 50 m.
The work described in this section was completed in con-
junction with Cerro Colorado Geologists., Chief Geologist,
and Mine Superintendent. The BHP-Billiton Base Metals
organization is gratefully acknowledged for support and per-
mission to publish this work.
14.1.2
Lithology
14.1.1
Geologic Setting
The present mapping and logging system uses five litho-
logical codes: Colluvium, Ignimbrite, Porphyry, Breccia,
and Andesite. No distinction is made of the different por-
phyries that have been identified in the deposit. Colluvial
boulder and conglomerate deposits of recent age overlay
The Cerro Colorado deposit is located within a north-trend-
ing belt of Eocene to Oligocene-age porphyry Cu deposits
(Cepeda et al.
1982
; Campbell
1994
). A thick sequence of
Cretaceous andesite tuffs, flows and agglomerates of the
