Pulacayo Project Feasibility Study - Apogee Silver

Pulacayo 1 000 t/d Phase I Feasibility Study - NI 43-101 Technical Report
090644-3-0000-20-IFI-100
7 GEOLOGICAL SETTING
7.1 Regional Geology
The regional geology of Bolivia is well described in various Bolivian government reports and
is summarized in technical reports completed for Apogee by Micon in 2008, 2009, and 2010.
The following regional geology description was extracted from the 2010 Micon report
(Pressacco et al., 2010) that in turn is based on translated content from an Apogee company
report (Iriondo et al. 2009) and US Geological Survey Bulletin (1975). The following text is
presented without change from Cullen and Webster (2012).
“In south western Bolivia, the Andes Mountains consist of three contiguous morphotectonic
provinces, which are, from west to east, the Cordillera Occidental, the Altiplano, and the
Cordillera Oriental. The basement beneath the area, which is as thick as 70 km, is believed
to be similar to the rocks exposed immediately to the east, in the Cordillera Oriental, where a
polygenic Phanerozoic fold and thrust belt consists largely of Paleozoic and Mesozoic
marine shales and sandstones (Figure 7.1).
Deposited mostly on Precambrian basement, the rocks of the Cordillera Oriental were
deformed during at least three tectonic-orogenic cycles, the Caledonian (Ordovician), the
Hercynian (Devonian to Triassic), and the Andean (Cretaceous to Cenozoic). The Altiplano
is a series of high, intermontane basins that formed primarily during the Andean cycle,
apparently in response to folding and thrusting. Its formation involved the eastward
underthrusting of the Proterozoic and Paleozoic basement of the Cordillera Occidental,
concurrent with the westward overthrusting of the Paleozoic miogeosynclinal rocks of the
Cordillera Oriental. These thrusts resulted in continental foreland basins that received as
much as 15,000 m of sediment and interlayered volcanic rocks during the Cenozoic.
Igneous activity accompanying early Andean deformation was primarily focused further west,
in Chile. During the main (Incaico) pulse of Andean deformation, beginning in the Oligocene
and continuing at least until the middle Miocene, a number of volcano plutonic complexes
were emplaced at several localities on the Altiplano, particularly along its eastern margin
with the Cordillera Oriental, and to the south.
In Pleistocene time, most of the Altiplano was covered by large glacial lakes. The great
salars of Uyuni and Coipasa are Holocene remnants of these lakes. The Cordillera
Occidental consists of late Miocene to Recent volcanic rocks, both lava flows and ash flow
tuffs, primarily of andesitic to dacitic composition, that have been erupted in response to the
subduction of the Nazca plate beneath the continent of South America. This underthrusting
continues, and many of the volcanoes that form the crest of the Andes and mark the
international border with Chile are presently active”.
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