Gastre, Argentina — Spectacular silver assay results highlight the new, grassroots Navidad discovery in the Patagonia region of southern Argentina.
Geologists for
Equally important is a more extensive style of disseminated, replacement mineralization that offers promising bulk-tonnage potential. Widespread galena mineralization was observed by the The Northern Miner during a site visit. It has been traced, in varying intensity in brecciated outcrop and subcrop, over a core area measuring 3.8 km long by 250 metres wide. This matrix style of replacement mineralization has yielded an average grade of 158 grams silver and 8.98% lead from a total of 41 randomly collected rock samples to date.
The high-grade structural zones, often obscured by a thin slope cover, occur in a core area measuring 160 by 110 metres. These steeply dipping structures form a series of sub-parallel, strongly mineralized zones hosted in a felsic unit. The felsic unit is believed to be a flow dome.
Keith Patterson, IMA’s exploration manager, avoids describing the high-grade structures as veins as they are not really open-face fillings. The exposed structures range in thickness from 0.2 to 5 metres, for an average of about 1 metre, and have been mapped over a cumulative strike length of 402 metres.
The average grade of 43 chip samples collected across the structures runs an impressive 6,537 grams silver (191 oz.), 3.5% copper and 16.6% lead. Paul Lhotka, a geological consultant to IMA, believes the geological potential for extending these zones is excellent, given that work to date has been hindered by the soil cover. No trenching has been done. Outside the Navidad hill area, several additional bonanza-grade structures have been found, and these contain some of the highest values to date.
Recently, a potential third type of mineralization was recognized near the margins of felsic volcanic units. It is a breccia containing replacement-style mineralization and copper oxides, with much higher silver grades. Sampling has returned values ranging from 205 to 6,012 grams silver, 0.1-14.9% copper, and 0.2-25.3% lead in 11 samples for which assays have been received to date. With each passing day in the field, the oxide copper is proving to be much more extensive than originally thought, says Lhotka.
IMA discovered Navidad in December 2002 while conducting preliminary field investigations of targets derived from a compilation of satellite data and regional maps. IMA geologist Daniel Bussandri came across the high-grade structures on his first day at the property, while walking up Navidad Hill. A fence line passes through the central part of the exposed high-grade mineralization, and boulders of rock containing obvious green copper staining have been used to prop up fence posts.
The Navidad area has no previously recorded occurrences of mineralization, nor is there any evidence the property has been explored (though it was briefly inhabited).
“There was not one hammer mark on anything,” says Lhotka. “You could walk past this from 50 metres away, but you could not walk on it and not find it. It’s impossible. You can see copper oxide on the top of the hill, and the rocks are so heavy you can’t pick them up.”
Adds Patterson: “In terms of ease of discovery, this is just obscene.”
Drawn to the southern region of Argentina by the multi-million-ounce, high-grade gold discoveries of Cerro Vanguardia and Esquel, IMA has been carrying out regional reconnaissance work in the Patagonia for almost three years, and to date has assembled a land package that exceeds 1,000 sq. km of properties.
The Navidad discovery occurs less than 1 km off a main gravel road in a tree-less, semi-arid part of the province, at an elevation of about 1,200 metres. From the road, the discovery area is pretty nondescript. There is no visible gossan or alteration to call attention to the area. Lhotka describes the climate as “cool temperate, quite dry and characteristically windy,” adding that “it’s pretty typical Patagonia country — fairly flat and rolling.” The closest town is Gastre, 35 km to the northwest, which has a population of roughly 500.
Underexplored
“A discovery of this type seems unthinkable in this day and age, especially within a few hundred metres of a provincial highway, until you realize that traditionally there has been a lack of mining and prospecting in the region,” says Lhotka.
A major high-voltage power line 45 km south of Navidad connects a hydroelectric dam at Futaleufu with an aluminum smelter at Puerto Madryn, a deep-sea port with shipping facilities 335 km to the east. The nearest railhead is 125 km to the northwest at Ingenerio Jacobacci in the province of Rio Negro. Esquel lies 200 km to the east-southeast.
The administrative unit is the Department of Gastre, which is one of the largest and least populated departments or counties in Chubut province. Locally, the only significant economic activity is sheep farming and government services.
“We identified the area as underexplored, and felt it had potential,” says Patterson.
The region does have a bit of mining history. The former-producing Mina Angela is 30 km northeast of Gastre. Mina Angela was a gold-silver-copper-lead-zinc mine that operated intermittently between 1920 and 1992, producing more than 1 million tonnes of ore from a series of polymetallic epithermal veins. Typical grades, according to Lhotka, averaged 2-3 grams gold, a couple hundred grams silver and 1-2% copper-lead-zinc.
“The people have good memories of that mining operation and the economic impact it had on the community,” says IMA President Joseph Grosso.
These are still early days at Navidad. IMA has acquired, by staking, a 100-sq.-km cateo. To the end of March, the junior had only 35 man-days on the property and had collected a total of 257 rock samples, 378 soils and 55 stream silts. IMA has proceeded cautiously since making the discovery, and has obtained written consent from two surface owners to carry out all necessary field exploration, including trenching and drilling. The company has also completed an environmental base-line study, which is required by the province of Chubut before exploration can proceed.
Geologically, the Navidad discovery is hosted in an Upper Jurassic series of mixed calcareous sediments and intermediate volcanics mapped by government geologists as the Canadon Asfalto Formation. This formation has never been the focus of metallic mineral exploration. Says Lhotka: “You wouldn’t go out looking for a Navidad, because there is nothing like it in the Patagonia.”
Mineralization occurs in what appears to be a sedimentary breccia containing clasts of sedimentary and volcanic origin. The breccia is intercalated with finer-grained, more tuffaceous equivalents and limestones of apparently marine origin. These rocks have been intruded by fine-grained, intermediate latite to dacitic igneous rocks, with features suggesting they are both intrusive and extrusive. They are interpreted to have reached the surface in a marine environment and contributed to the clasts in the breccia.
Intercalated with the breccia unit are thin but extensive siliceous and calcareous beds, which are believed to be exhalite units and which are anomalous in silver, copper, lead, zinc and arsenic. Based on their presence, Lhotka suggests that the hydrothermal system responsible for Navidad vented to the surface in a marine environment.
IMA’s geologists believe the Navidad system is part of a shallow subaqueous epithermal system that deposited metals at or near the sea floor. The high-grade structures in the felsic flow dome appear to represent “feeder” structures to mineralization that comprises extensive areas of sulphide replacement of unconsolidated volcanic breccias.< P>The surrounding galena matrix mineralization is believed to have replaced a pre-existing matrix of the unconsolidated breccia. Patterson says the heterolithic breccia was derived predominantly from material that shed off the flanks of the felsic domes. The breccia was porous and permeable, making it a nice host for mineralizing fluids that came along and replaced the matrix to the breccia. Of note, rare clasts or fragments of massive sulphides have been found re-sedimented in the breccia, which Patterson says suggests a possible stratiform massive sulphide source.
Navidad is unique in that it is extremely silver-rich and contains virtually no pyrite or iron sulphides. Preliminary petrographic studies on surface samples indicate the Navidad Hill bonanza-grade structures contain fine-grained argentite-acanthite, galena, chalcocite and lesser copper-silver-lead chlorides and oxides. The replacement-style mineralization consists almost entirely of silver-bearing galena; no discrete silver minerals have been identified.
IMA believes Navidad is geologically similar to precious-metals-enriched, volcanogenic-massive-sulphide systems with epithermal characteristics, such as the Eskay Creek mine in northern British Columbia. Patterson, who spent three years at Homestake looking for another Eskay Creek, says: “This is closer to anything we ever found.”
IMA continues to carry out rock and soil sampling, in addition to property-scale geological mapping, in an attempt to define drill targets. The company is set to begin a ground geophysical program consisting of 70 line km of induced-polarization (IP) surveys. The program will include a couple of test lines of gravity. The IP survey will be configured to show up the galena in the replacement-style mineralization, while the resistivity portion is expected to highlight the high-grade structures.
Preliminary soil sampling has been conducted over a strike length of 5 km along north-south-oriented grid lines spaced at 200 metres, with samples collected at 50-metre intervals. Outside the Navidad hill area, soil sampling has identified a highly anomalous area of 1,200 by 500 metres, with values consistently greater than 2 grams silver per tonne. These high silver values correlate well with anomalous copper values of greater than 50 parts per million (ppm) and compare favourably to the high silver-copper values at Navidad hill.
Highly anomalous lead values, consistently greater than 500 ppm, occur naturally in the soils and define a 4-km-long trend that correlates with, and potentially expands, the known replacement-style silver-lead mineralization. Several areas stand out from the soils, including areas where values of up to 531 grams silver and 574 ppm copper have been recorded.
The company has also stepped out from the property and is conducting reconnaissance sampling along a 40-km-long trend. “It should give us an idea if there is anything else as obvious as Navidad that we ought to jump on to,” says Patterson.
With winter fast approaching in the Patagonia, IMA’s exploration team is going full out until June or so, when they will take a break before resuming field work in early September.
On the back of the promising Navidad discovery, IMA recently closed a $2.6-million private placement of 2.9 million units priced at 90 apiece. Directors and officers of the company took down $1.2 million. Each unit consists of one share and a half-warrant. The financing boosts IMA’s kitty to $4.2 million. The company currently has 32.5 million shares outstanding, or 43.1 million on a fully diluted basis. Major shareholders include
IMA has been exploring for gold in Argentina and Peru for almost a decade, under the guidance of Joseph Grosso, who founded the company in 1993. At the outset, Grosso teamed with the Vicente Mendez, the former head geologist of Argentina’s state owned mining agency, and aggressively assembled a highly prospective package of early-stage properties. Today, the company holds a portfolio of 37 projects and properties, including the drill-ready Rio Tabaconas gold project in northern Peru, which was put on hold in mid-2002 so that the company could improve upon community relations in that region. In addition, IMA holds a 2% net smelter return royalty on
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