Local Geology

The local geology of the Bramaderos region is poorly understood compared to other parts of the country. The geology of the region is discussed in relation to the Cariamanga 1:100,000 map sheet.

At this local scale, the geology is dominated by the Cretaceous volcaniclastic sediments belonging to the extensional Celica-Lancones basin, and which are intruded by the Cretaceous-age composite Tangula Batholith. The dominantly granodioritic Tangula Batholith has metamorphosed the surrounding Cretaceous sediments.

The Celica Formation in the region inter-tongues with the overlying Alamor Formation  and occurs across the Bramaderos property and south of it. It comprises submarine andesitic volcanic rocks that represents the products of a volcanic arc of Albian (lower Cretaceous) age. The best sections of the Celica Formation Lower Cretaceous arc series (over a 1000m thick) and its sedimentary cover are located in the fault-bounded Rio Playas depression west of Catacocha.

In detail the Celica Formation (which hosts the porphyritic and subvolcanic intrusions at the Bramaderos project) consists of massive lava flows, welded tuffs, pillow breccias, conglomerates and agglomerates of mainly andesitic composition with some intercalated limestone lenses.   

The overlying Alamor Formation is poorly defined and poorly understood and may represent the upper part or a lateral equivalent of the Celica Formation.

Higher in the sequence the 150-200m thick Naranjo Formation unconformably overlies the Celica or Alamor volcaniclastic rocks. The lower parts comprise pebbly and fossiliferous calcareous marls and coarsens upward into marls, fossiliferous limestones and greywacke beds.   

The Casanga Formation (200-400m thick) overlies the Naranjo Formation and comprises turbiditic greywackes with nodular limestone.

Unconformable continental deposits overly the Casanga Formation and comprise purple-coloured red-beds and volcanic rocks including continental shales, siltstones and volcaniclastic beds that crop out east of El Naranjo.

The Rio Playas Formation – could be restricted to yellow-coloured sediments (conglomerates, sandstones and shales) that unconformably overly the undated red beds, the Casanga or Alamor Formations.          

The unconformable continental deposits and Rio Playas Formation could be westward lateral equivalents of the Sacapalca Formation of Palaeocene to Eocene age. The Sacapalca Formation east of the Bramaderos project comprises thick sub-aerial andesitic tuffs and agglomerates with fluvial red-beds in the upper parts. Near Nambacola, Catamayo and Catacocha, capping fluvial red-beds on top of the Palaeocene-Eocene Sacapalca Formation might correlate with the undated unconformable continental deposits and Rio Playas Formation described above.       

Finally, a series of porphyritic diorite stocks and plugs intrude the Celica Formation within the Bramaderos property. Similar stocks are shown further east penetrating the Sacapalca Formation, and so these were considered to be of Tertiary age. However, historical dating of a quartz-diorite stock at Curiplaya, obtained a U/Pb age of 92 +/- 1.0 Ma which concluded the Curiplaya porphyry intrusions as being Cretaceous age.