Geology
- Regional Geology
The following discussion of the regional geology is compiled and modified from reports by Richards et al. (1999), Smith (2001), and Kesting (2002). The western part of the Salta province is underlain by mid to late Tertiary continental volcanic arcs and related sedimentary rock of the Andean cycle. The Andean Volcanic Arcs are concentrated along the north trending axis of the high Andes and along several northwest trending “structural transverse zones”. Sedimentary rocks are deposited in large back arc continental basins similar to the huge Siete Curvas basin, a portion of which is active and includes the large Salar de Arizaro (Figure 5).
Basement is dominated by high to medium grade metamorphic rocks of Proterozoic age, which are exposed south of the basin. Cambrian-Ordovician granites and granodiorites form a magmatic belt oriented north south, outcropping east and south of the Salar de Arizaro. Cambrian to Ordovician platform-shelf clastic sediments with submarine volcanic facies of the Famatinian cycle are exposed east of this basin and generally these units have a north south trending grain.
The area west of the Salar de Arizaro is also underlain by Cambrian to Ordovician intrusive rocks mainly characterized by course grained granites. In the same north south magmatic belt, Permian to Jurassic granitic intrusive rocks and spatially related dacite volcanic rocks and rhyolite-rhyodacite porphyritic rocks of Eocene-Oligocene age are present. All these units are covered by Pliocene volcanic rocks of the north south Andean Volcanic arc. North of the Salar de Arizaro, Silurian to Permian continental and shallow marine clastic sedimentary rocks appear, forming part of an uplifted structural block.
The Siete Curvas basin is bounded to the north and south by northwest transverse volcanic arcs of the Andean cycle. The Catua and Arizaro-Lindero properties are located within one of these northwest trending tertiary volcanic belts; near the south edge of the Salar de Arizaro. These volcanic belts are characterized by subjacent or superimposed stratovolcanic complexes; commonly manifested today as eroded stratovolcanoes consisting of andesite to dacite porphyries and coeval volcanic rocks including ignimbrites, pyroclastic tuffs and volcaniclastic rocks.
The Siete Curvas basin, a 100 km wide by 130-km long extensional basin, which includes the Salar de Arizaro, occupies the central zone. This basin consists of continental sedimentary rocks including immature red beds, extrusive volcanic rocks and significant evaporite deposits; suspected to be active since early Tertiary.
Structurally, the Siete Curvas basin is bounded by large, regional normal and strike-slip faults. The bounding structure on the north is the northwest trending, “Calama-Olacapato-El Toro Transverse Zone” and on the south is the northwest trending “Archibarca Transverse Zone”. The transverse zones are interpreted to be the surface expressions of ancient deep crustal trans-lithospheric structures, which have been periodically reactivated and possibly related to the initial opening of the Proto Atlantic Ocean during Cretaceous times. The “East Fissure Fault Zone” and the “Pocitos Linear” bound the basin to the west and east respectively. These regional north-south trending structures are believed to represent suture zones of previously accreted terranes; a geotectonically similar situation to the “West Fissure Fault Zone” in Chile.
Intersections of these regional structures appear to create favourable tectonic preparation for the locus of mineralizing systems. These deep-crustal structures have undergone complex, episodic movements related to ongoing subduction, which has created permeable conduits that have focussed magmatic activity which in turn has provided a heat source for fluid movement. The combination of these fundamental basics is critical for the development of hydrothermal deposits, similar that documented for many of the world-class porphyry copper deposits in Chile. For example, the world-class Escondida copper deposit lies at the intersection of the “West Fissure Fault Zone” and the “Archibarca Transverse Zone”, while the El Abra and behemoth-sized Chuquicamata Cu porphyry systems are located at the intersection of the “Calama Transverse Zone” and the “West Fissure Fault Zone”.
Similar structural intersections localizing magmatic-hydrothermal systems have been documented at the Cerro Samenta copper porphyry prospect and the Arizaro-Lindero gold-copper porphyry prospects. The Rio Grande Cu-Au deposit lies within the north to northeast trending “East Fissure Fault Zone” (Figure 6).
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