International mining company Southern Hemisphere Mining Limited (TSX VENTURE:SH)(ASX:SUH) has reported encouraging results from the initial 8-hole reverse circulation drilling program at one of its priority copper exploration projects in Chile, the El Arrayan Project, located in the highly prospective Coquimbo Region.
Results have so far been received for six of the eight holes (1,800m) completed to date as part of the drilling program, which commenced in mid December 2010. From the assay results received, copper mineralisation was recorded in four of these six holes and significant intercepts were recorded in Hole EA002.
These included a composite weighted average for significant intercepts of 65m @ 1.00% Cu in Hole EA002. This composite weighted average contained several higher grade zones which included 26m @ 1.54% Cu, including an internal intersection of 17m @ 2.03% Cu.
Location
The El Arrayan Project concessions are located in the Province of Elqui, which is part of Chile's Region IV, and are only 37km south east from the regional capital of La Serena and neighbouring major Port of Coquimbo. The concession area covers approximately 64 sq kms.
The Project lies just 15km north-northeast from the Andacollo porphyry copper mine, which is owned by Teck Cominco.
Regional Setting
The El Arrayan Project lies within the Coastal Cordillera of north-east Chile in a north-northwest trending structural corridor, that extends for some 150km from south of Andacollo to Los Choros Creek in the north.
Mineralisation
The El Arrayan style of mineralisation resembles Andacollo with a diorite intrusive being the source of mineralisation, although a large percentage of the mineralised zone is in the adjacent andesitic wall rocks, with propilitic alteration (chlorite, epidote, calcite, specularite), sericitic alteration, and combinations of both types.
The El Arrayan mineralization consists of copper oxides, and minor chalcopyrite with pyrite and magnetite. A preliminary stage geological interpretation shows that the mineralisation could be a mixture of veins and mantles associated with porphyritic diorite intruding volcanic-sub-volcanic sequences of fine grain andesite with minor microdiorites.
This mineralisation could represent the medium-distal part of a hydrothermal system, probably associated with a copper-gold porphyry target, similar to the Andacollo porphyry copper system.
The copper-gold porphyry systems are characteristically associated with diorite-tonalite intrusives with moderate to weak quartz-sericitic alteration and rich in magnetite-specularite-quartz veinlet systems. All these characteristics have been observed in the Project area.
The model for El Arrayan mineralisation is similar to the Andocollo system, which has a reserve base of approximately 500 million tonnes with a grade of 0.44% Cu and 0.13g/t gold.
Ongoing drilling will test this copper/gold porphyry model.
Analysis
Assay samples from the reverse circulation drilling program were taken at one metre intervals from splits of the drill chips, using a standard sample splitting system at El Arrayan. Sample preparation and analysis was conducted on 4-5 kg drill samples by Andes Analytical Assay Ltda ("Andes") in Santiago, using Atomic Absorption Spectrometry methods. Andes is an independent full service commercial laboratory accredited under ISO 9001:2008. Control samples were inserted by Andes and every 10th sample was repeat assayed.
From the results to date, four of the six holes intercepted mineralised zones and the remaining two drill holes were found to fall outside the mineralised zones.
Detailed Results
An intercept of 26m, between 86m and 112m, returned an average grade of 1.54% Cu. Within that intercept, between 86m and 103m, an intercept of 17m returned an average grade of 2.03% Cu. The most significant intercepts shows a composite weighted average of significant intercepts for Hole No EA002 of 65m at 1.00% Cu.
The analysis results for the remaining two drill holes will be disclosed separately when received.
The intercepts between the reported significant intercepts above consisted of Fine Grained Andesite or Porphyritic Diorite and produced a composite weighted average assay grade of 0.02% Cu.
Source: Southern Hemisphere Mining Limited