Canaima, Venezuela — The La Camorra mine in southeastern Venezuela is set to pour its millionth ounce at the beginning of the second quarter. This milestone will be closely followed by a new era of production with the completion of a 600-metre vertical shaft (the mine has used ramp-access up until now).
Travelling down the ramp, it isn’t hard to imagine the advantages of a shaft. For starters, it currently takes one hour to descend to the lowest level (about 620 metres below surface). That time will be reduced to a few minutes. The company expects to haul 3.6 tonnes of ore at a time, up the shaft to surface, at a speed of 1,255 ft. per minute. Sixty tonnes of ore per hour will be transported to surface over a 10-hour period, rather than the current 24 hours it takes to haul about 450 tonnes.
Shaft construction began in November 2003; the shaft is 4.5 metres in diameter and, as at presstime, was slashed to 400 metres deep. The total planned depth is 625 metres, though the headframe, drum hoist and auxiliary equipment have a rated 3.6-tonne capacity from a depth of 1,145 metres.
The main access ramp is between the Main and Betzy zones. The shaft is a couple of hundred metres west of the Main zone.
The mine currently produces 12,200 tonnes of ore per month grading 20 grams gold per tonne. Drilling is under way to firm up the proven and probable reserve to 70% of the total resource, but for now the mine plan is based on 260,000 proven and probable tonnes grading 22.75 grams gold per tonne and 260,000 inferred resources grading 21.5 grams gold per tonne. These resources are restricted to the Main, B1 and Betzy veins.
La Camorra is hosted by an Archean to Proterozoic greenstone belt. Near-vertical auriferous quartz veins are mined. The veins are in a regional west-northwest shear zone but strike in various directions; that is, the Main vein strikes northeast whereas the Betzy strikes east.
The major veins are often only about 40-50 cm wide, though occasionally they widen to about 1 metre.
The Main vein comprises four ore shoots plunging to the west at 65. Some of these zones are characterized by single, discrete veins, while others contain multiple anastamosing structures.
The Betzy vein is a banded quartz vein with a central ore shoot with a strike length of 100-150 metres. Numerous smaller discontinuous ore shoots are found east of the vein.
Visible gold is common and can be seen in drill core, and in quartz veins at the face of the drifts underground. Gold is also locally associated with chlorite and may be attached to, or within, pyrite.
Hecla has used data from the past 16 years to identify targets for exploration. The company recently performed magnetic, induced polarization and resistivity surveys. Soil geochemical surveys have identified sizable gold anomalies (mimicking auriferous veins) within a few hundred metres of the Main zone. Eight holes have been drilled into the Isbelia vein, about 700 metres north of the mine. Assays are pending.
Exploration drilling is being directed at the Main zone at depth (between the 850- and 1,000-metre levels). Several targets are about 300 metres below existing development and in locations that are more easily drilled from surface using precise directional drilling technology. Eight holes will test the eastern side of the Main zone between the 425- and 625-metre levels. Other lateral drilling has added 20 metres to the strike of the B zone.
La Camorra produced 154,124 oz. gold in the first nine months of 2004 at a cash cost of US$165 per oz.
Isidora
About 5 km southwest of El Callao, Hecla is preparing to test-mine gold at the Isidora project, which forms part of the company’s Block B area concessions.
Isidora is just west and downdip of the El Chile mine, which produced 600,000 oz. gold in the period 1870-1940.
The Pozo de Agua, at the past-producing El Chile mine, is an inclined shaft that is being rehabilitated for the test mining of Isidora’s resource. A ramp is being developed (it is currently 200-300 metres long) to gain access to the Isidora deposit, and once it is complete, the shaft will be used as a second exit and ventilation shaft. During the test-mining phase, Hecla will mine about 50 tonnes of ore per day.
Production at the daily rate of 400 tonnes is slated to begin in 2006.
Since late 2002, Hecla has drilled 131 holes (35,850 metres) into the Isidora resource. Twenty-one holes that cut the M vein graded between 1 and 10 oz. gold (nine others graded from 14 to 29 grams gold). The average width of the vein is 1.5 metres. Twelve of the holes that intersected the S vein cut grades greater than 1 oz. (highlighted by a 0.91-metre intercept that graded 871 grams gold), and nine additional holes graded 13-25 grams gold per tonne.
At April 2004, Isidora had a proven and probable resource of about 570,000 tonnes grading 29.7 grams gold per tonne. The main resource is hosted by the M and the S veins.
In general, the footwall of the Isidora mine is a magnetic basalt, and the hanging wall may be pillowed basalt or fragmental flow units. Intermediate-to-felsic porphyry dykes tend to trend north-northwest and dip east, though they are also found paralleling the M vein (and form its hanging wall). The S shear and associated vein are 8-20 metres into the footwall of the Main shear that hosts the M vein.
The El Chile mine produced most of its gold from the J vein, which ran sub-parallel with the M vein and stratigraphically above it. Within the Main shear, the J vein pinched out, though a mineralized structure to the east may be its downdip extension.
The whole zone is structurally complex. Major shear zones and local faults traverse the area. The El Callao shear trends toward the northeast in the Isidora-Chile area and dips at 45-60. The east- to east-northeast-trending Isidora-Chile zone dips to the south at 45.
Typical veins are massive and ribboned quartz veins with chlorite, sericite, pyrite and free gold. Minor gold-silver-bismuth tellurides are present locally. Quartz veins have been altered, and fractures contain ankerite and sericite (porphyry dykes are believed to be the source of the sericite alteration) and gold.
Exploration
Systematic regional exploration has focused on east-trending structures, which locally tend to swing northwest. Three types of mineralization are being targeted: quartz veins with free gold, quartz veins with pyrite (up to about 5%), and shear zones with pyrite in veinlets.
Geological mapping has focused on structural trends. Numerous prospects are being tested using magnetic, induced-polarization, and geochemical surveys. Three target areas — Chile East, Twin-Conductora and Eureka — have been drilled. In each of these areas, the amount of gold is proportional to the percentage of pyrite.
The Chile East main shear zone was mined by previous owners to a depth of less than 100 metres. The area is brecciated and faulted, and Hecla tested the shear at depth. Both the main shear zone and a second structure are 5-10 metres thick and characterized by 15-40% quartz-stockwork veins with ankerite and/or sericite and 5-25% pyrite. Significant assays from nine drill holes grade from 6.4 to 19.8 grams gold per tonne over widths of 1.4-8.7 metres.
One kilometre northeast of the Isidora mine, the Twin-Conductora shear zone has been tested by 42 holes (40,500 metres of drilling).
The Twin shear runs east for a few hundred metres before swinging north and following an east-northeast trend. The shear zone is 20 metres wide, at least 1 km long, open on both ends, and cut by faulting. Gold mineralization (from 6 to 16 grams gold per tonne) has been intersected over widths of 2-12 metres. Folding is evident in the footwall. Within the shear is strong ankerite and/or sericite and chlorite alteration.
The Conductora shear may be an extension of the Twin. Drilling has tested it along a strike length of 700 metres, highlighte
d by a 12-metre intercept grading 14 grams gold per tonne. Another hole cut 10 metres grading 12 grams gold. The zone was found during a reconnaissance mapping program, which was followed up by geochemical and geophysical surveys. Drilling is ongoing.
A weak induced-polarization anomaly with a coincident geochemical anomaly was also drilled, resulting in intercepts up to 10 metres wide grading 4 grams gold per tonne (another hole cut 9.6 metres grading 3.65 grams gold).
Small miners, working in partnership with Hecla, are producing ore at a couple of deposits north of the Twin-Conductora area — at Santa Rita and Panama.
Partnerships
Setting Hecla apart from other companies working in this region is its philosophy of co-operation with “small miners,” who often work the ground illegally.
The company decided to make the best of a conceivably discordant situation by setting up a sampling plant where the miners can bring their ore and have it crushed and sampled; a representative assay is then determined, and then the miner is given the option of having Hecla mill the ore. If the miner agrees, the ore is trucked to Hecla’s mill at La Camorra (a distance of about 100 km), where gold recovery is much higher than the small mills that are otherwise available to the miners.
In some cases, Hecla is helping to finance the mining; there are 20-30 larger-scale miners, of which Hecla is financing 17-20. The miners often work on new veins in old mines. The company finances them until they produce, and also provides technical services. The material goes to the sampling plant, and after costs have been split, the profit is divided. Hecla takes a percentage to recover the money it is investing in the operations.
“The system is well-organized and -controlled,” says David Howe, Hecla’s vice-president of Venezuelan operations. “In return, we get social peace, great relations with these guys, and access to all of these veins. Their technology, even if we help them out, isn’t going to take them below about 60 metres from surface. This gives our exploration guys more information than we would get by drilling a few holes.”
The company is improving living standards in nearby communities. Hecla has two Venezuelan sociologists on staff who work as community relations managers. Improvements have been made to area schools and electrical lines in the town of El Callao.
Driving from the town to the site, The Northern Miner observed numerous houses with concrete water cisterns in their yards; these were white with “Hecla” stenciled in blue. The company has built 70 such tanks to date, and water is delivered at regular intervals — an improvement over previous conditions.
The company has put in a 7-km-long access road, which will bypass communities in the area. The road enables ore to be transported from the Isidora mine to the mill at La Camorra.
The Block B property is leased from Minerven, which owns 3%. There is also a net smelter return royalty of 3% and a mining tax of 3%.
Be the first to comment on "Hecla to step up production at La Camorra in Venezuela"