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Location
The Mamañina property lies on the east side of the Cordillera Blanca, at elevations of between 3,900 and 4,650m, approximately 580 km north of Lima near Hauraz. It lies along the same narrow belt of mineralised Miocene intrusive rocks as the world-class Antamina copper-zinc skarn deposit and the Magistral project.
Title
Monterrico Metals has acquired a 100% interest in the property from Queenstake Resources (70%) and Duran Ventures (30%). This property consists of two claims; "Magistral 3" (1000 ha), which covers the main areas of mineralisation and which is owned by Corporacion Minera Vulcan S.A. and "IRI 215" (400 ha) which is owned by Compañia Minera IRI Peru S.A. and acquired as a potential mill site and tailings area.
Geology
The prospect contains both copper-zinc skarn and copper-molybdenum ± gold bearing porphyry type mineralisation within a sequence of Upper Jurassic and Lower Cretaceous marine sedimentary rocks deposited in a basin lying between the Coastal batholith zone to the west and uplifted Precambrian and Palaeozoic metamorphic rocks to the east. These host rocks consist of quartzites, siltstones, slates, shales, limestones and dolomites which have been intensely folded and over-folded along a north-westerly striking trend during an early Tertiary orogeny. Within the mineralised area these folds have a localised east-west trend thought to be the product of an underlying deep-seated transverse fault structure.
A cluster of high-level porphyry stocks and dykes of granodioritic to monzonitic composition intrude the sedimentary rocks. Many of these felsic intrusives exhibit phyllic (sericite) and potassic (biotite) alteration. Quartz vein stockworks, containing disseminated pyrite and chalcopyrite, are associated with some of these stocks as are bodies of breccia containing clasts of granodiorite, skarn, quartzite and mineralised siltstone within a matrix of quartz, skarn minerals and sulphides.
Impure carbonate rocks have been metamorphosed and metasomatised by felsic intrusions to form pyroxene-garnet skarns, hornfels and mantos within overturned synclinal structures. Skarn hosted mineralisation is primarily pyrrhotite, pyrite, chalcopyrite and sphalerite as disseminations or as veins while more massive mineralisation occurs within the mantos.
History
Copper mineralisation was identified in the area in October 1995 by Queenstake geologists undertaking a helicopter reconnaissance to check anomalies revealed by Landsat imagery. In 1996 follow-up reconnaissance mapping and sampling located mineralised skarns and porphyries. This led to the more systematic coverage of the area in 1997, which involved both rock chip and soil sampling campaigns and defining a series of geochemical anomalies along a 1.8 km belt. Copper, zinc and gold were found associated with skarns and manto deposits closely associated with tight synclinal structures immediately overlying, and intruded by, a granodioritic intrusion while copper and molybdenum were associated with porphyry stocks. Later in 1997 ground geophysical surveys (magnetometry and induced polarisation) were undertaken in conjunction with detailed geological mapping and, together with the geochemical data, allowed the recognition of four main copper targets and a gold target which partially overlaps a 1,000 by 700m area of potential Cu-Zn skarn/manto mineralisation. This latter area appears promising with geophysical responses indicating mineralisation penetrating to depths of at least 250m and with geological evidence suggesting a buried porphyry beneath, and to the south west of, the skarns. This area is believed to have the potential to host a large base-metal deposit. The other targets (on Cerro Rojo, Cerro Mantos and on the west flanks of Cerro Sur) are equally attractive.
Monterrico completed a scout programme of five diamond drill holes in October 2002, focusing exclusively on testing the anomalous copper geochemistry shown at surface. Drilling intersected high-grade copper mineralisation, including 25m at 1.65% copper from 14m below surface. Low-grade gold mineralisation was also discovered in the same hole.
Development
An initiative to test the potential for a gold resource in the southern sector of the property, indicated by a widespread geochemical anomaly, is currently being considered by management. At the same time the Company is accepting expressions of interest from other mining companies with the objective to form a joint venture via a drill commitment.
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