Buenaventura
Location
Buenaventura is located 50 km NNE of Copiapó, between Freeport's Candelaria and Anglo American's Manto Verde copper mines.
Ownership
In April 2008, Mariana and Minotaur Exploration Ltd (Minotaur) announced a joint venture with Sociedad Minera Contractual Buenaventura (Buenaventura CSM) whereby they could jointly earn 51% by spending US$3M over 3 years and 80% by completing a bankable feasibility study with additional rights to bring in a funding partner and first refusal over the remaining 20%. In February 2009, Minotaur had to withdraw because of company-wide exploration cutbacks. Mariana remained in the joint venture with Buenaventura CSM.
Geological Setting
The 44km2 project is situated along the Atacama Fault Complex, which hosts all major Chilean iron oxide-copper-gold (IOCG) deposits. Favourable host rocks of the Punta del Cobre Formation are present, together with four centres of IOCG type copper mineralization (intense hydrothermal alteration, brecciation and both hematite - copper and magnetite - copper association).
Previous Exploration
Previous drilling (2005/2006) completed by Buenaventura CSM focused in and around these outcrop areas. IOCG type copper mineralization as oxide (upper levels) and sulphide (deeper levels) was encountered in a number of holes, from near surface to depths of up to 400m, with intervals ranging from 10 to 90m and grades generally in the range 0.2 to 0.5% copper with gold up to 0.13 g/t.
Exploration by Mariana
In 2008, Mariana and Minotaur expanded and infilled a 2004 gravity survey to locate dense bodies of iron oxides. Four residual gravity anomalies were highlighted. An anomaly stood out in the NE coinciding with the Cerro Brecha Copper-Gold Prospect, a 2km2 area of hydrothermal breccias, extensive hematite, copper oxides and strong faulting. Past drilling intersected up to 28m @ 0.43% Cu, 0.13 g/t Au. 3D inversion modeling of the Cerro Brecha gravity anomaly by Minotaur indicated a significant dense mass at depth, below previous drilling, possibly an iron oxide body. A deep hole was planned for Q1 2009 but was not drilled after Minotaur’s withdrawal. Mariana subsequently reviewed the 3D modeling, which confirmed the major drill target at Cerro Brecha. Other targets were identified at Cerro Berta based on geology, geochemistry and magnetics.
Drilling
Targets at Cerro Brecha and Cerro Bertha were drill tested in Q4 2009.
Two RC percussion holes at Cerro Berta Norte tested coincident magnetics, alteration, brecciation, hematite, strong fracturing and anomalous Cu, Au and Co in soils over a 1.5 x 1km area. Hole BV-RC-01 was drilled to 500m and encountered anomalous copper and gold from near surface to 440m, with the highest assays returning 6m @ 0.32% Cu plus 0.44g/t Au from 374m.
The second hole (BV-RC-02) was terminated at 358m due to technical problems, however anomalous copper was encountered throughout, with the bottom 90m averaging 415 ppm Cu and 23 ppb Au.
At Cerro Brecha, a single deep hole tested the upper part of an anomaly interpreted to be dense iron oxides (from 3D modelling of the 2008 gravity survey) below known shallow IOCG type copper/gold mineralization from previous drilling. BV-RD-01 was drilled as a pre-collared diamond hole to 651m. It intersected hematite and minor magnetite (10-20%) from 180-234m with anomalous copper (120-1500ppm) from 210-272m. In the cored section, the rock is mainly an andesitic breccia with anomalous copper mineralisation (chalcopyrite) intersected from 454-490m (120-1500 ppm Cu).
On-going Exploration
A review of exploration to date indicates new targets. Further exploration may include additional geophysics.
Buenaventura - Geology
Buenaventura - Cerro Berta and Cerro Amada Alterartion
Buenaventura - Geology of Cerro Brecha
