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Location Map - IRN Projects - Northern Chile
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PBA & PS - Geology - CSAMT Anomaly Trends
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PBA & PS - As in Colluvial & Soil & Float - CSAMT Anomaly Trends
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PBA & PS - Sb in Colluvial & Soil & Float - CSAMT Anomaly Trends
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PBA & PS - Au in Float & As in Colluvial & Soil - CSAMT Anomaly Trends
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PBA & PS - Ag in Float & As in Colluvial & Soil - CSAMT Anomaly Trends
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PBA & PS - CSAMT Resistivity at - 50m - CSAMT Anomaly Trends
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PBA & PS - CSAMT Resistivity at - 100m - CSAMT Anomaly Trends
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PBA & PS - RTP Magnetics (Grey) - CSAMT Anomaly Trends
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PBA & PS - RTP Magnetics (Colour) - CSAMT Anomaly Trends
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PBA & PS - Principal Geochemical & Geophysical Anomalies - Priority Ranking
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PBA & PS - Aster Image - False Colour
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The Pampa Buenos Aires project covers approximately 27,000 hectares and approximately 18km of continuous strike length of the prospective Dominador Fault Zone (DFZ). The project is located approximately 15km southwest of Yamana's Peñon and Fortuna deposits (+7 million oz gold and +200 million oz silver), and immediately north of Iron Creek's Pampa Sur project. The DFZ lies within the Palaeocene-Eocene volcanic belt of northern Chile that hosts some of the most important precious metals and copper deposits in the country.
The Pampa Buenos Aires properties are subject to a joint venture agreement between Compañía Minera Mena Resources (Chile) Limitada -- Iron Creek's Chilean subsidiary (Iron Creek), and Andina Minerals Chile Limitada (Andina Minerals) where both companies own 50% of the joint venture company, Sociedad Contractual Minera Pampa Buenos Aires. The Shareholders Agreement was signed on August 14, 2008 and Iron Creek is currently operator of the joint venture company. This agreement was preceded by a Letter of Intent between the two companies that was signed in August 2006.
Iron Creek and Andina Minerals are exploring the Pampa Buenos Aires (PBA) property for epithermal gold and silver mineralization of El Peñon/Fortuna and Guanaco types, and also for possible porphyry copper mineralization.
Geological Setting of Pampa Buenos Aires
The property is largely covered by post-mineral gravels with sparse outcropping Palaeocene-age volcanic rocks towards the southwest of the property area. The property is cut by strands of the DFZ, which defines the structural grain of the project area.
The Palaeocene to Early Eocene Volcanic Belt of northern Chile underlies much of the Atacama Desert in the Antofagasta and Atacama regions of northern Chile. The belt extends north-south for about 600km and is bounded to the west by the Coastal Cordillera and to the east by the Domeyko Cordillera. The geology of the belt is dominated by Late Cretaceous to Early Tertiary calc-alkaline to sub-alkaline bimodal volcanic rocks that range from basaltic andesite to rhyolite, and by sub-volcanic porphyritic intrusions and granitoid stocks.
The portion of the belt between Sierra Gorda in the north and Sierra Overa in the south, which includes Pampa Buenos Aires, is characterized by exposures of felsic volcanic rocks, and is host to several precious metal epithermal deposits including the El Peñon and Fortuna gold-silver deposits, as well as other significant precious metal deposits at San Cristobal, Faride, El Soldado, Cachinal de la Sierra, El Guanaco, Amancaya and Sierra Overa.
Cerro Buenos Aires Exploration Target
Cerro Buenos Aires is a prominent hill of 1,890m altitude located in the SW corner of the property, rising about 300m above the surrounding post-mineral gravels that cover much of the large PBA property. The Cerro Buenos Aires target is underlain by Mid-Palaeocene (60-58 Ma) mafic volcanics that are crosscut by a 57-55 Ma rhyolite dome complex that coincides with the summit of the hill. The rhyolite dome complex covers an area of approximately 4km2 at surface. The mafic volcanics and rhyolite dome are intruded by younger andesite porphyries along the north-western slopes of the hill. Hydrothermal alteration is represented by widespread and pervasive silicic-argillic alteration. Patches of strong silica and haematite alteration are mainly located at the intersection of conjugate fractures sub parallel to the DFZ. The younger andesite porphyries outcropping along the north-western slopes are affected by propylitic alteration only.
Historic exploration, mostly carried out during the 1980s, was focused on porphyry copper models and high-level, silica-cap hosted precious metals targets.
Cerro Buenos Aires probably represents a high level of exposure of a moderately eroded Palaeocene hydrothermal precious metals system. This is supported by the increasing intensity of hydrothermal alteration towards the Cerro Buenos Aires dome, the surface geochemistry with high arsenic, antimony, mercury and rare precious metals values, and the occurrence of haematite-bearing silicification on top of the hill that likely represents the remnants of an eroded silica cap developed at the palaeo-water table.
Cerro Buenos Aires consequently represents a valid target for low-sulphidation epithermal veins, and the hydrothermal alteration and associated geochemical anomalies at surface probably represent the highest level "leakages" of such a system. However, productive veins are likely to be found at some depth beneath the current outcrops -- perhaps 300m to 400m. The local topography would allow for easy operational access to these proposed deeper veins, through an incline from the surrounding pampa.
Cerro Blanco Exploration Target
Cerro Blanco consists of a relatively isolated hill in the northeast corner of the PBA property, located some 8km east of the DFZ, surrounded by post-mineral gravel-filled pampas. Cerro Blanco has been considered as a porphyry or epithermal target for some time and was subject to exploration by several copper exploration companies in the 1980s, with some drilling carried out in the surrounding pampas but not on the hill itself. Host rocks appear to be mostly highly altered mafic volcanics, with some possible felsic intrusive rocks, cut by late, fine grained, mafic dykes.
Hydrothermal alteration at Cerro Blanco is dominated by an advanced argillic assemblage of pyrophyllite + kaolinite +/- dickite together with some silicification to the west, and a more sericite-dominated alteration assemblage to the east. This would indicate that the outcrops at Cerro Blanco represent the base of a lithocap to a porphyry system. This interpretation is strengthened by the identification of "wormy" quartz veining within a pyrophyllite +/- kaolinite matrix, which has been described at other localities (e.g. Yanacocha) as being a transition texture between the porphyry and epithermal environments. The "lithocap" alteration does not necessarily lie vertically above the source porphyry intrusion; indeed the source porphyry might lie at some distance from the remnant lithocap outcrops.
Surface outcrops are affected by supergene oxidation and leaching giving rise to extensive supergene jarosite and haematite, with some supergene alunite, kaolinite and gypsum.
Two Iron Creek drill holes from 2008 at Cerro Blanco confirmed the continuity of likely porphyry-related hydrothermal alteration at depth, including advanced argillic alteration assemblages in hole PBA033, and a magnetite + quartz + pyrite stockwork within an intrusive rock in hole PBA032. The magnetite found in hole PBA032 is the likely source of a small magnetic anomaly located underneath Cerro Blanco. The rest of the alteration seen at surface and in drill holes is magnetite-destructive and corresponds to a large magnetic low feature surrounding the small magnetic high. Future drilling to depths of at least 750m is likely required to fully test this porphyry target.
Work Completed To Date
Upon signing of the LOI between Iron Creek and Andina Minerals in late August 2006, Iron Creek initiated an aggressive exploration program consisting of geological mapping, float mapping and sampling, a 300 line km ATV supported geochemical pH and colluvial/soil sampling survey (approximately 12,000 samples), and revision of time domain electromagnetic and aeromagnetic geophysical surveys (approximately 1,400 line kilometers) acquired by Newmont in 2001-2003. Additionally, during September 2006, Argali Geofisica E.I.R.L. conducted an induced polarization (IP) and resistivity survey at Cerro Blanco consisting of one line of 5.4km length.
From this work, seventeen target areas were identified to be drill tested. Thirteen corresponded to structural targets assumed to be related to epithermal vein mineralization, and four corresponded to possible magnetite-rich intrusive events with perceived potential for porphyry mineralization. Further work during 2007 and 2008 included more geological mapping, geochemical and geophysical surveys and, in 2008, 8,032m (33 holes) of exploration RC drilling, the latter focused on ten targets which represented about 60 % of the total targets defined at that point in time within the PBA project area. These targets, located within a narrow, 20km long prospective structural zone around the trace of the DFZ, have mostly been tested with no more than one or two drill holes per target.
The drilling completed in 2008 targeted sub-cropping, low-sulphidation precious metal quartz-calcite veins (Target H); geochemical anomalies (Targets F and R); structural features associated with the DFZ (Targets A, BC, DE, G, J and Q); and one possible magnetite-rich intrusive with potential for a high-sulphidation or porphyry type system (Cerro Blanco -- Target M).
Following on from work carried out from late 2006 to end 2008, a decision was taken during 2010 to expand reconnaissance geochemical pH and colluvial/soil sampling surveys with widely spaced lines (1km), over the entire post-mineral covered portion of the PBA property. This surveying (1,250 samples) was completed in October 2010. Additional surveying comprising 1,480 soil and talus (sieved -10 mesh) samples collected on a 50m x 100m grid over the Cerro Buenos Aires hill, was completed in December 2010. These surveys were intended to better define targets for geophysical profiling and drill testing over the entire property package.
During May and June of 2011, approximately 55 line kilometers of Controlled Source Audio-Frequency Magnetic-Telluric (CSAMT) surveying were completed along five east-west oriented survey lines. Additionally, several samples of quartz-vein float material lying on the surface of the gravel-covered pampas were collected in several locations.
Results to Date
Results from the 2008 drilling were mixed, although the two Iron Creek drill holes at Cerro Blanco confirmed the continuity of likely porphyry-related hydrothermal alteration at depth, and other targets revealed modest anomalies and mineralised structures. Many of the drill holes on targets close to the DFZ were affected by this major fault structure. Mineralised vein structures at El Peñon and Fortuna, for example, are located along structural splays some distance from the main DFZ trace. The more recent geochemical sampling surveys are intended to look for targets further away from the main DFZ trace.
Results from the colluvial and soil geochemical programs at PBA, including Cerro Buenos Aires, are particularly encouraging and show partially coincident arsenic and antimony geochemical trends, somewhat supported by mercury anomalies, as can be seen from the accompanying maps on Iron Creek's website. A 2km long arsenic and antimony anomaly extends along the crest of the Cerro Buenos Aires hill. Intermittent anomalies extend for a further 2km giving a 4km long anomalous trend in total. Minor mercury and silver anomalies accompany the arsenic and antimony. Some 6km further to the north, in an area largely covered by post-mineral gravels, a strong north to north-northeast trending arsenic anomaly occurs with minor antimony anomalies. To the east of the DFZ, also in areas mostly obscured by post-mineral gravels, several broadly coincident arsenic and antimony geochemical anomalies occur. Some of these anomalous trends are supported by sporadic mercury, zinc, copper and silver anomalies.
An important arsenic and antimony geochemical anomaly in the south-central part of the property, immediately to the east of the DFZ, is open to the south-southeast and is contiguous with a significant anomalous trend on Iron Creek's Pampa Sur property.
Arsenic, antimony and mercury are three of the key pathfinder elements for El Peñon/Fortuna style, low sulphidation epithermal precious metals veins. None of the priority arsenic/antimony/mercury geochemical anomalies defined here coincide with previous drilling carried out by the joint venture partners on the property.
Other smaller anomalies of one or more of these key indicator metals occur within the property, and may prove to be significant.
Also of interest from the geochemical data is a large area of molybdenum and zinc anomalism in the gravels in the north-eastern quadrant of the property. This anomalism is centred on the Cerro Blanco area, where outcrops display advanced argillic hydrothermal alteration styles typical of the higher erosional levels of a porphyry copper system.
The quartz-vein float material sampled in several locations occurs along linear trends coincident with some of the principal colluvial and soil geochemical anomalies, and CSAMT anomalies. The assay results show that many samples are anomalous in gold, silver, arsenic and antimony. Arsenic and antimony are common pathfinder elements for low sulphidation quartz veins.
The CSAMT survey was designed to: 1) follow-up extensive surface colluvial and soil geochemical anomalies on the property; 2) to help define the normally resistive features that may host epithermal quartz veins beneath the extensive post-mineral gravel cover; and 3) to test for similar features beneath the silica cap at Cerro Buenos Aires.
The CSAMT survey has defined a series of relatively high resistivity anomalies, some of which are continuous between profiles despite the wide line spacing. Critically, some of the best CSAMT high resistivity anomalies coincide with strong surface colluvial and soil geochemical anomalies, suggesting that they may reflect silicified zones or structural features related to potentially mineralised veins at depth. At Cerro Buenos Aires, a significant series of resistivity anomalies coincide with the outcropping silica cap which is interpreted to represent the highest levels of an epithermal system. Importantly, a series of deeper, sub-vertical high resistivity anomalies indicate the possible presence of epithermal-related alteration zones beneath the silica cap. Cerro Buenos Aires is highly anomalous at surface in arsenic and antimony, with minor mercury, silver and gold.
The principal geophysical anomalies were determined from both the CSAMT modelled profiles, and from a series of modelled depth slices of resistivity at -50m, -100m, -200m and -300m depths. These principal geophysical anomalies were integrated and compared with the known geochemical anomalies, historic airborne and ground magnetics data, and with mapped geology and areas of hydrothermal alteration.
The combination of the geochemical and geophysical results is extremely encouraging. Major anomalous trends occur in both data sets, and many of the principal anomalies are wholly or partially coincident. The occurrence of metal-bearing epithermal quartz-vein float material, and in the case of Cerro Buenos Aires an outcropping silica cap, coincident with some of the principal geochemical and geophysical anomalies may indicate the presence of silicified zones or structural features related to potentially mineralised veins at depth.
Qualified Person:
Demetrius Pohl, P.Geo., is the Company's Qualified Person as defined by National Instrument 43-101, and is responsible for the accuracy of the technical information in this project summary. Dr. Pohl has verified that it is an accurate summary of the results from the Pampa Buenos Aires exploration programme.
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