Sierra Blanca Gold-Silver Project
- Location: Middle of the highly prospective Deseado Massif, Santa Cruz province. Approximately 140 km WSW of Las Calandrias Project and 50km. NW of AngloGold's Cerro Vanguardia low-sulphidation epithermal gold mine.
- Mariana interest: 100% with 1.5%NSR to IAMGOLD
- Area: Approximately 7,000 hectares.
- Prospect type: Intermediate-sulphidation epithermal silver + gold
- Latest: Fourth drilling campaign of 5,273m completed December 2011.
Sierra Blanca and (nearby) Cañadon Largo originally formed the Santa Cruz JV (Mariana 70%, IAMGOLD 30%). Mariana exercised it’s right to acquire the remaining 30% from IAMGOLD Inc. for US$500,000 in cash and shares in Mariana to the value of US$500,000. In return IAMGOLD receives a 1.5% royalty on net smelter returns from any future production. Mariana now controls an undivided interest in the properties.
Approximately 15,000m of drilling has been completed to date. Encouraging epithermal style gold-silver mineralization was discovered at Veta Chala in Q4 2008 with a best intersection of 11.0m @ 3.4 g/t Au and 386 g/t Ag from 46m in hole SBD51.
The Sierra Blanca prospect is largely hosted by the El Tranquilo and overlying Roca Blanca Formations (Upper Triassic and Lower Jurassic respectively). They underlie the Bajo Pobre and Chon Aike Formations; the Jurassic volcanic sequences that host most of the epithermal precious-metal deposits in the Deseado Massif.
The El Tranquilo Formation comprises epiclastic sandstones and siltstones with prominent carbonaceous mudstones which dip shallowly eastwards. The Roca Blanca Formation is lithologically similar but flat lying.
The epithermal mineralization in the Sierra Blanca district appears to be related to a felsic porphyry dome that underlies the northern end of the Vetarron zone. The porphyry is relatively unaltered, but is partially surrounded by jasper cemented phreatic breccias, the formation of which is believed to have accompanied dome emplacement.
The principal fault is ENE. The Chala vein lies just south of this fault whereas, farther west, the Lucila vein is located immediately north of it. In contrast, the El Tranquilo veins strike NW, and the Vetarron zone follows a north-south trend (Fig. 1). The Chala Central vein dips steeply north Blanca Formation in the hanging wall. In contrast, the Lucila vein dips steeply north and appears to be within the Roca Blanca Formation.
First pass exploration by IAMGOLD identified epithermal quartz veins over a 7km strike with rock chip assays of up to 1.1 g/t Au and 635 g/t Ag (Lucilla Vein).
Geological mapping, rock chip sampling and prospecting by Mariana in 2006 discovered quartz veins/vein breccias trending for at least 12km and an inferred 29km.
Scout drilling (2,523 m) in early 2007 tested targets at Sierra Blanca and Cañadon Largo. Of 22 holes, 18 tested eight veins strongly anomalous in gold, silver and pathfinder elements, consistent with high-level epithermal silver-gold systems. Ten holes intersected multi-stage quartz veins but six did not reach the planned target. Despite disappointing results, Mariana persisted and discovered new veins at Vetarron and Cero Bola. Mariana’s IP/Resistivity and magnetic surveys indicated numerous prospective silicified structures, many with coincident changeability responses.
Subsequent prospecting discovered a 1.2km+ E-W trending vein system at Veta Chala, in the NE Sierra Blanca area with bonanza silver and gold in channel samples with up to 9.4 m @ 2,362 g/t Ag 1.3 g/t Au.
Follow up drilling in late 2008, included 28 RC drill holes (2,120m) and eight diamond drill holes (550m) at Veta Chala, Lucila and Vetarron, totalling 3,005m. The drilling at Veta Chala discovered encouraging epithermal style gold-silver mineralization. Best intersections included 11.0m @ 3.4 g/t Au and 386 g/t Ag from 46m in hole SBD51, 14.3m @ 2.8 g/t Au and 242 g/t Ag from 31m in hole SBD55 and 21.0m @ 0.7 g/t Au and 189 g/t Ag from 33m in hole SBR27.
Early in 2011 Mariana completed 5,181 metres of diamond drilling (31 holes) mainly at Veta Chala. Twin hole CHD59 intersected high grade silver mineralisation at Chala Splay target in eastern Veta Chala – 4.2m @ 1.2 g/t Au and 420 g/t Ag from 74.6m.
Wide zones of manganese-carbonate-quartz-sulphide vein breccias were discovered at the Achen vein system (formerly Chala West) with up to 3m @ 9.5 g/t Au and 28 g/t Ag within 28.7m @ 1.4 g/t Au and 11 g/t Ag from 85m (CDH61). Achen is composed of banded quartz, adularia, rhodochrosite, rhodonite and sulphides with typical intermediate sulphidation epithermal textures over a 450m strike. The vein system has been drilled to only b130m and is concealed under extensive gravel cover to the west. A possible link with the Lucila vein 2km away is indicated by a prominent linear magnetic low.
A fourth drilling campaign commenced at the beginning of October 2011. Initial targets from previous drilling and geophysics include Veta Chala, Lucila and Vetarron.
|CHD61||28.7m @ 1.4 g/t Au, 11.5 g/t Ag from 85.0m
including 3.0m @ 9.5 g/t Au, 28 g/t Ag from 87.0m
|CHD71||- 20.3m @ 1.5 g/t Au, 34 g/t Ag from 121.7m
including 2.65m @ 6.8 g/t Au, 23 g/t Ag from 135.6m
|CHD72||14.5m @ 1.2 g/t Au, 17.2 g/t Ag from 126.5m
including 6.0m @ 2.5 g/t Au, 18 g/t Ag from 135.0m
Chala Central and Chala Splay
|CCHD79||3.2m @ 406 g/t Ag and 0.7 g/t Au from 67.0m (Chala Splay)|
|CHD57*||19.9m @ 0.5 g/t Au and 11 g/t Ag from 64.8m (Chala Central)|
|CHD59*||4.2m @ 1.2 g/t Au and 420 g/t Ag from 74.6m
including 0.5m @ 3.2 g/t Au & 813 g/t Ag from 77m (Chala Splay)
|CHD84||30.1m @ 2.2 g/t Au and 101 g/t Ag from 23.0m
including 2.9m @ 1.8 g/t Au & 666 g/t Ag from 27.4m
and 2.1m @ 15.9g/t Au & 38.5 g/t Ag from 41m (Chala Central)
|SBR27||21.0m @ 0.7 g/t Au and 189 g/t Ag from 33m
including 2.0m @ 2.7 g/t Au & 1,435 g/t Ag from 46m (Chala Central)
|SBD51||11.0m @ 3.4 g/t Au and 385 g/t Ag from 46m
including 2.8m @ 12.7 g/t Au & 1,172 g/t Ag from 50.2m (Chala Splay)
|SBD55||14.3m @ 2.8 g/t Au and 242 g/t Ag from 31.7m
including 1.5m @ 15.2 g/t Au & 775 g/t Ag from 40.7m (Chala Splay)