The Frontera property hosts historical resources of 16 million indicated tonnes grading 0.38% copper and 0.22 grams per tonne (“g/t”) gold and 34 million inferred tonnes grading 0.36% copper and 0.22 g/t gold. The historical resource estimate was prepared by Hot Chili Limited based on 16,175 metres of drilling completed in 2013.
| Frontera Cu/Au Deposit - Historical Resource Estimate (March 2014) | |||||
| Classification | Tonnes | Cu | Au | Contained Metal | |
| (millions) | (%) | (g/t) | Cu (‘000 lbs) | Au (ounces) | |
| Indicated | 16 | 0.38 | 0.22 | 134,400 | 116,000 |
| Inferred | 34 | 0.36 | 0.22 | 275,500 | 239,000 |
| The historical resource was prepared by Hot Chili Limited under “Australasian Code for Reporting on Exploration Results, Mineral Resources and Ore Reserves” (The JORC Code, 2012 Edition) and published on March 11, 2014. The resource estimate is based upon a cutoff grade of 0.25% Cu. ATERRA’s qualified person has not completed a full audit of the historical resource estimation procedures and, therefore, this historical resource should not be relied upon as it is not a current mineral resource under NI 43-101. | |||||
The Frontera copper-gold deposit is hosted within a dacitic to dioritic porphyry which lies within a north-northeast trending zone of dacitic stocks, sills and dykes that were probably emplaced at intersections or dilation zones of major structures associated with the Atacama fault zone. Fine grained secondary sericite (after feldspars) is present and mineralization consists of copper oxides and sulphides, dominantly chalcopyrite, and minor magnetite along with significant gold values. The host porphyry is believed to be Late Cretaceous, based on relationships with surrounding rocks, and the similarities with other well-documented intrusives of this age within the immediate area.
Frontera Mineralization and Alteration
The most important economic copper mineral at Frontera is chalcopyrite, which in the porphyry is the dominant copper mineral present. Chalcopyrite occurs as very fine to extremely fine disseminations in quartz-K-feldspar veinlets and coalescing alteration haloes, and rarely as thin veinlets. At the surface, copper oxides are found sporadically in veinlets within the stockworked zone. Secondary enrichment does not play a significant role at Frontera with regard to copper, or alternatively the enriched zone has been eroded. Within the weakly enriched zones, minor chalcocite and covellite have been reported.
The Frontera deposit exhibits alteration assemblages indicative of the mid-level domain of a typical porphyry copper system with alteration dominantly as muscovite (sericitic) and albite (sodic), with chalcopyrite-rich, pyrite-poor material clearly associated with strong potassic alteration.
Photo: Strongly altered and overprinted porphyritic diorite composed of altered phenocrysts of plagioclase and recrystallized quartz. The groundmass is composed of quartz and plagioclase grown pseudomorphs. Alteration is composed of feldspar with superimposition of sericite and clay, with addition of polycrystalline and recrystallized quartz. The rock is cut by veinlets filled with quartz, pyrite, chalcopyrite, tourmaline, chlorite and sericite (Macdonald, J. Lachlan and Leighton, Melanie; Frontera Resource Report, Hot Chili Limited; February 2014)