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ORONORTE PROJECT AREA
(MACHUCA (FRAGUAS)-ZARAGOZA- EL BAGRE GOLD DISTRICT)
ANTIOQUIA, COLOMBIA
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GEOGRAPHIC LOCATION & ACCESS
The project is located at the northern end of Colombia’s Central Cordillera, three km south of the town of Zaragoza in the northeastern portion of the Department of Antioquia. Access from Medellín, is by mostly paved road through Remedios and Segovia to Zaragoza (280 km, 10 hours) or by 40 minute daily commercial flight from Medellín to El Bagre, and hence from El Bagre along secondary roads and the Nechi River to Zaragoza, the mine area, and the other known prospects.
REGIONAL PRODUCTION HISTORY
The northeastern region of the Central Cordillera of Colombia including, the Serranía de San Lucas, is, and has historically been, Colombia’s preeminent gold mining district. It was gold mining activity in this region that generated an accumulation of wealth in the Department of Antioquia during the 19th century and allowed the expansive industrial development of the Central Colombian region, based out of Medellín. This historic region is contained within a gold producing belt which stretches for over a 150 km from Santa Isabel in the south through Remedios and Segovia to Zaragoza, El Bagre and Caucasia in the north. The region remains a major contributor to the national production of gold and silver in Colombia.
The northeastern Antioquia region contains some of the longest-lived gold mines in Colombia. Some of these operations include:
Mineros of Antioquia, formerly Pato Gold Mines de Colombia Ltda., (an early facet of Placer Development Inc.) has operated since 1906. Mineros of Antioquia mines the auriferous alluvial deposits of the Nechi River. This general region (known as the "Lower Cauca region") has produced over 25 million ounces of alluvial, colluvial and in situ gold.
Frontino Gold Mines Ltda. have been active in the Segovia and Remedios regions for almost 160 years, principally mining high-grade mesothermal vein deposits (a partial source of the Lower Cauca alluvials). Tese areas have recorded production on the order of 8 million ounces troy Au, about half of which has come from a single vein system, the "El Silencio", which has produced over 4 million ounces Au. Frontino presently mine from the "El Silencio", and "Providencia" vein systems.
Choco Pacifico Mining Co: Anglo American’s Colombian operations, active until the 1960’s were focussed upon alluvial platinum and gold production in the Choco, and the mining of numerous high-grade vein occurrences around Remedios and Zaragoza. They produced well over one million ounces in their operations, including about 150,000 ounces Au from the El Limón Mine at Zaragoza (as detailed below).
The Remedios through El Bagre, including the Oronorte area, remains a highly active artisanal and semi-mechanised alluvial, colluvial and hardrock-vein mining region, and accounts for a good percentage of the zones gold production. Miners work as highly efficient and organized groups with investments in operations that reach approximately US$600,000 in equipment (bulldozers, backhoes etc.), extracting gold using a variety of gravity circuits commonly combined with rather crude mercury and cyanide extraction techniques. These "informales" as a rule do not comply with the national environmental legislation or the Colombian mining code.
GEOLOGY and MINERALISATION
The northeastern Antioquia region is underlain by rocks of primarily Precambrian, Paleozoic and Jurassic ages, and is divided by a series of major fault zones belonging to the Palestina-Bagre-Nus-Otu system. The Precambrian rocks include quartzo-feldspatic gneiss containing sporadic lenses of amphibolite and marble. The amphibolites are observed as foliaform lenses possibly representing deformed sills or dykes. The Paleozoic rocks are observed to occur over extensive areas, especially to the west of the Otu Fault, and include intercalated quartzites, marbles, and quartz-sericite (locally graphitic) and chlorite schists, all of upper greenschist metamorphic grade. To the south and east the quartzites are intruded by the polyphase, calc-alkalic Jurassic Segovia Batholith of dioritic through granitic composition. To the east of the Otu Fault, the left-lateral El Bagre Fault separates rocks of the Segovia Batholith from Proterozoic gneiss and migmatite farther east. Intercalated, unconsolidated Tertiary and Quaternary sands, gravels and clays partially cover the area, lapping onto the low ridges of the western Serranía de San Lucas. These sediments are widely exploited for their contained alluvial-colluvial gold.
The regional structural geology is dominated by the Otu-Bagre fault system, a series of important crustal-scale, left lateral strike-slip structures which strike broadly north-south. These faults separate at least two allocthonous continental megaterranes comprised of slivers and fragments of the Guiana Shield, demarcating a Proterozoic accetionary complex. Vestiges of the actual suture zones are indicated by the occurrence of serpentinites and deep oceanic meta-sediments along these structures. Reactivation of the structures during subsequent orogenic events in the Andean region of Colombia generated adequate structural and rheological conditions which allowed for widespead magmatic emplacement, the circulation of hydrothermal fluids, and mineral deposition in associated transtensional regimes.
Mineralisation in the historic Remedios – Segovia – Zaragosa gold belt is controlled by the Otu Fault, which at this latitude strikes N10W. To the south, in the highly productive Segovia and Remedios gold camps, abundant mineralisation is contained within second-order structures associated with a N30W flexure in the Otu Fault. A similar flexure is observed at the El Limón mine and within the Oronorte Project area in general. Mineralisation is hosted within all of the rock-types underlying the northeastern Antioquia region, as described above.
The style of gold mineralisation throughout the region is generally mesothermal, characterised by high-grade, quartz-dominant poly-event vein systems hosted within first, second and third-order dilatencies and joint sets associated with major structural breaks. Veins host 2 to 20% mixed base metal sulphides (pyrite, pyrrhotite, sphalerite, galena, chalcopyrite) and native gold. Silver – gold ratios range from 0.5 to 2 to 1, and minor telluride minerals are not uncommon. Alteration is developed in broad halos about the structural breaks, and is dominated by regional propylitisation and carbonitisation containing concentrated zones of pyritic or pyrrhotitic sulphidation and silicification related to gold mineralisation. Grade – depth continuity of mineralisation is one of the striking features of the vein deposits of the region. The El Silencio vein, for example has been mined continuously for over two km along strike and two km down dip (to level 38), and production continues.
RESOURCE DEVELOPMENT AT ORONORTE
EL LIMON MINE
The historic El Limón Mine was discovered by H. Von Stauffen, who, in 1939, compiled the first exploration report for the Minera Timmins Ochali Company of Montreal, Canada (this same company exploited the Berlín Mine, Antioquia between 1920 y 1932 and produced ca. 500,000 oz Au). Between 1948 and 1961 El Limón was exploited by the Choco Pacifico Co. (Anglo American) who developed five levels from the current zero level via room and pillar methods, and produced about 150,000 oz Au. Subsequently, Mr. Von Stauffen worked the mine intermittently until 1975.
In 1986 Greenstone Resources Inc., a Toronto, Canada-based company, initiated exploration below the zero level and via the development of a shaft and a drilling program outlined new reserves. They built a 120 ton/day plant which through crushing, milling and floatation produced metallic concentrates grading 500 to 800 g/ton Au, and containing an equal amount of Ag with minor Pb, Cu, and Zn. When Fischer-Watt Gold Co. Inc. acquired the operations in 1995, a cyanide circuit was installed (allowing Au recoveries of +90%) and doré was produced on-site. Greenstone – Fischer Watt production totaled approximately 56,000 oz Au.
The El Limón Mine has been developed on six levels. It has been worked down to the fifth level and a portion of level six has been exploited through short declines from the fifth level. The mine has the handling capacity to deliver 80 ton/day to the mill, limited by multiple ore handling problems. However, the outfitting of an existing, but out of service, 370 meter-long decline that connects level zero with level six, will allow for the rapid delivery of 200+ t/day of ore directly to the plant. Present mill and plant capacity (ca. 100 tpd) can rapidly be expanded to meet this increase.
Based upon drilling results and underground development to mid-1997, an independent audit of the EL Limón resource base by Watts, Griffis and McOuat, Lakewood, Colorado, indicated proven and probable reserves of 156,674 t @ 15 g Au/t (+75,000 oz Au). Based upon additional drilling and underground development to Dec., 1999, Fischer Watt placed indicated reserves at 197,230 t @ 16.5 g/t (+100,000 oz Au, see table below).
Potential for depth continuity of the El Limón mineralisation, as seen at El Silencio, Segovia, is excellent. Based upon structural modeling carried out at El Limón by consulting geologist Craig Byington, drilling completed by Fischer Watt in the Juan Vara sector of the vein system some two km south from the present mine workings, intersected 40 cm of mineralised structure averaging 43 g Au/t.
EL CARMEN AREA
El Carmen is located 12 km to the northeast of the El Limón Mine. Early exploration data by Dual Resources of Canada was acquired by Greenstone Resources, and the project was subsequently transferred to Fischer Watt and the Grupo de Bullet S.A. Surface and trench sampling and 3,600 metres of exploration drilling were completed by Dual, which indicated a mineralised structure of over 2 km in length cutting a granitoid intrusive, hosted within a zone of tectonic reactivation of probable Jurassic age. Mineralisation is contained within a series of ca. N-S-striking veins ranging from 50 cm to 5 metres in thickness which dip 60E and contain average gold values of 11.5 g/ton. The granitoid has been mapped for almost 5 km in a north-south direction and averages 700 meters in width. It is cut by parallel N-S stiking quartz veinlets, and a series of andesitic to dacitic (rhyolitic?) dykes. The quartz veinlets have widths of 1 to 3 cm. Veinlet-hosted and disseminated pyrite, galena and sphalerite are observed.
Exploration development by Dual on the southern end of the principle El Carmen structure included a 30 metre decline and approximately 30 metres of drifting following the vein strike. Based upon the 3,600 metres of core drilling, the underground development, and additional surface work, Greenstones Resources, 1993, calculated indicated reserves over the 2 km strike length of the principle structure at El Carmen including 737,472 tons averaging 11.5 g/ton (273,043 oz Au). This calculation extrapolates the structure to a depth of 100 meters (up to the area of influence of the Dual drilling).
Additional drilling in 1997 by Fischer Watt at El Carmen proved additional depth continuity to the principle mineralised structure. Results of this program included an intersection of 53 cm grading 493 g Au/t, which prompted Watts, Griffis and McOuat to comment, in their independent audit of the area, that the average grades quoted at El Carmen to date may be lower than those which will eventually be encountered in underground development work.
Assuming the structure extends to 500 meters depth (as seen in many mines in Segovia and Remedios), one million ounces of Au resources can be envisioned. Additionally, as presented above, excellent bulk-mineable potential within the El Carmen granitoid body has yet to be fully exploration tested.
GOLD RESERVES AT ORONORTE AS OF DECEMBER 31, 1999
RESOURCE POTENTIAL
The marked historic through modern-day interest of a wide range of gold exploration and production companies, including Placer Development Inc., Anglo American Gold, TVX Gold, Latin Gold Inc., Metallica Resources Inc., Procoloro Ltd., Fischer Watt Inc., Greenstone Resources Ltd., and Dual Resources Ltd., and numerous private Colombian national companies, is indicative of the potential of the Oronorte project area. With respect to the overall gold potential of the region two indisputable facts must be born in mind:
The region reports multi-tens-of-million-ounce gold production, historically second to none, anywhere in Latin America.
In the region there exist numerous undeveloped gold showings which support a vibrant artisanal mining scene within a gold-prolific geologic framework, which has, from a modern-day standpoint, scarcely been reconnoitered.
Geologically, the Palestina (Otu-Bagre-Nus) fault system structurally controls a gold mineralizing system of over 500 km in strike length, extending from the central portion of the Central Cordillera, between Tolima and Caldas through northern to Antioquia. Hydrothermal gold and polymetallic mineral manifestations are well known throughout this region. Many have extensive production histories, others remain simple manifestations or prospects, with undefined potential.
Aside from the key Oronorte projects discussed above, numerous additional gold showings are found in the Oronorte – Zaragoza area, many of which are located within the Oronorte claim area. Most of these prospects have only received superficial investigation which indicate they definitely warrant further exploration. For more information, please contact:
J.W. Asociados Y Cia Ltda
Cra. 25 #36-D Sur 135
Medellin, Colombia S.A.
(574) 336 1655
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Copyright © 2005 John Wood. All Rights Reserved