Mexico: Tropico Project
Skeena Resources Limited has acquired 100% equity interest in the 27,000+ hectare Tropico copper-platinum-palladium-gold project in Sinaloa State, Mexico. The property is exceptionally well located with respect to low-cost infrastructure, being crossed by two paved highways, two major powerlines, within 10 km of the N-S coastal rail line, and 30 km north of the deep water port of Mazatlan.
The property covers a steeply NNW dipping, ENE striking (ie: at a right angle to the regional trend of the Siera Madre Occidental to the east), 19 km long by 1 to 3 km wide, Late Jurassic to Early Cretaceous layered mafic/ultramafic igneous complex that intrudes Paleozoic schists (metasediments). The complex is cored by pyroxenite, or mixed pyroxenite-gabbro, which in turn is enclosed by gabbro. It is intruded by Late Cretaceous to Early Tertiary diorite, which is locally cut by quartz diorite to granodiorite (possibly part of the Sinaloa Batholith). Late stage Oligocene volcanics overlie much of the Complex (particularly the southern contact).
The primary exploration targets are large tonnage, open pitable, low-grade zones of disseminated copper sulphide mineralization with associated platinum, palladium and gold values. To date, known occurrences are preferentially deposited proximal to gabbro-pyroxenite contacts in stratigraphically controlled zones where there is a change from predominantly plagioclase cumulate to pyroxene cumulate (both at the hangingwall and footwall contacts of the pyroxenite or mixed pyroxenite-gabbro core). There is some potential for massive, high-grade, copper-nickel-platinum-palladium-gold occurrences in "feeder-pipe" zones or along major faults or within fold structures.
Historically, the project area has been subjected to considerable prospecting, soil geochemistry and ground geophysics, originally for nickel by BHP Minerals in the late 1990's, and subsequently, additional geochemistry, extensive mechanical trenching and drilling during the period 1999 to 2002, by a joint venture comprised of Santoy Resources Ltd. and Almaden Minerals Ltd. of Vancouver. This latter work was largely financed by Sumitomo Metal Mining Co. Ltd. of Japan. Historic expenditures are in the order of $5 million.
To date, nine sulphide occurrences have been identified at Tropico, consisting of variable, sparse amounts of chalcopyrite, cubanite, bornite, pyrrhotite, pyrite and minor pentlandite. This is a low sulphidation system -- generally with less than 2 to 3% total. Some of the better mineralized trenches at the Maricela Occurrence were reported to assay 0.50 to 1.00 % copper and up to 1 gram/tonne combined platinum + palladium + gold (generally with a platinum to palladium ration in the order of 0.75:1) over widths of 15 to 160 metres. Some 39 drill holes totaling approximately 6,550 metres are reported in the Santoy-Almaden Joint Venture ("the JV") summary report (28 core holes by the JV). The best reported drill intercepts were 0.5% Cu and 0.75 g/t over 38.9 metres (hole M-02-08) and 0.39 % Cu and 0.55 g/t Pt+Pd+Au over 128.1 metres (hole M-01-03) at Maricela; and 0.54% Cu and 0.52 g/t Pt+Pd+Au over 47.0 metres and 0.82 % Cu and 0.70 g/t Pt+Pd+Au at San Pablo (hole SP-02-01).
The project was terminated by the Santoy -- Almaden -- Sumitomo JV in December 2002 due to depressed metal prices (copper at $0.75/lb., platinum at $590/oz., palladium at $230/oz., and gold at $345/oz.) and a proposed follow-up drill program was never initiated.
In 2008, the Company contracted Fugro Airborne Surveys to undertake a helicopter-borne DIGHEM multi-frequency electromagnetic and magnetic survey (1,100 km of 100 metre spaced lines) of the property. The survey coverage and orientation was designed to investigate down-dip areas of known mineralization and those areas covered by a thin mantle of recent volcanics. This data is currently being re-processed and will be compiled with the existing database.
In 2010, the Company undertook the emplacement of approximately 170 line kilometers of soil sample grid (approximately 3,500 new samples acquired on historic grid extensions and in-fill lines, generally at 50 metre station intervals and 100 metre spacing). 31 element analyses (identical procedures as the historic sampling) by Acme Laboratories in Vancouver has now been received and plotted. The compiled soil geochemical database now includes in excess of 7,650 samples. Additionally, approximately 500 lithogeochemical samples were acquired as part of a three month geological mapping program.
A schematic compilation of all soil geochemical sample results, prior trench results, and all diamond drill intercepts is presented on 4 map sheets on Skeena's website.
In the late fall of 2010, the Company commenced a limited back-hoe trenching program (targets set out on the map sheets noted above). This is approximately one third complete, and will be re-initiated in late 2011.
The current 5,000 metre diamond drill program is focused on the apparently geochemically and geophysically continuous, 5,000-metre-long Maricela-San Pablo Zone, which has previously been explored by 22 trenches and 18 drill holes, and the 1,500-metre-long El Pochote zone, which was investigated by four trenches and two drill holes. These two zones characteristically occur along a low ridge crest with sparse overburden and tree cover in an area bounded by agricultural fields. The zones appear to be good, potentially open pit targets in a district with excellent infrastructure.
The Maricela-San Pablo Zone was previously explored with 21 backhoe trenches -- all of which intersected good mineralization over significant widths (refer to news release dated March 1, 2011). The zone has been further tested with 24 historic drill holes -- of these two were vertical (with no platinum group metal (PGM) assays having been completed), one vertical hole was outside the zone, six angle holes were outside of the zone, one reverse circulation hole was drilled at right angles to the zone, seven holes were drilled down dip and only six holes appear to have been successfully drilled at the proper orientation. Furthermore, three gaps of 800 metres, 900 metres and 1,000 metres along strike remain undrilled. The El Pochote zone is less explored.
Tropico appears to be a classic, layered, mafic/ultramafic complex. When the historic and current multielement soil geochemical database of 7,651 samples is geospatially and statistically analyzed, the most striking observation is the enrichment and the strong interelement correlation amongst copper, nickel, cobalt, chrome, platinum, palladium and gold. The correlations and metal ratios are typical of sulphides segregating from a moderately to highly fractionated basic magma with possible alkaline affinities. Furthermore, there is no evidence of any significant supergene enrichment. The more mobile copper and palladium are strongly correlative with the more immobile nickel, chrome, cobalt and platinum.
The complex appears to be dipping to the north-northwest (at least in the Main Maricela-San Pablo area) at approximately 80 degrees as indicated by modeling and profiling of the Fugro DIGHEM airborne magnetic survey data.
This first phase of drilling is being targeted at proving up lateral continuity to the zones (primarily by infilling the three historic gaps) to a vertical depth of 150 to 200 metres.
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