Silver Bull Resources (TSE:SVB) (AMEX:SVBL) provided Tuesday an update on a planned 3,000 metre underground drill program to target a high grade zone of silver at its Sierra Mojada project in Coahuila, Mexico.
The company said the campaign will target a high grade silver area with grades up to 472 grams per tonne (g/t) of silver over 17 metres within the Shallow Silver Zone at the project.
The high grade zone was defined by historical long hole drilling and channel samples, the company said.
Of the 150 long holes that defined the zone, Silver Bull said 75 have average weighted intercepts of more than 80 g/t silver, and include 472 g/t silver over 17 metres, 447 g/t silver over 9 metres, 348 g/t silver over 21 metres, 322 g/t silver over 16 metres, and 363 g/t silver over 10 metres.
Over 70 per cent of the long holes that defined the area ended in mineralization. Long holes are drill holes averaging between 10 to 20 metres in length that "grind" through the rock to produce a "rock chip" sample and underground channel samples.
The silver and zinc miner also noted that the 500 metre east-west trending strike of the high grade zone remains open toward the east.
Silver Bull plans to start a 3,000 metre underground drill program targeting this 500 metre-long high grade zone of silver in the middle of this month.
There are 2,700 long holes within the historical data set that defined the zone, representing more than 37,873 metres of drilling.
The company said, however, that the impact of the long hole data on its latest NI 43-101 resource update on the Shallow Silver Zone in late May was "severely restricted" due to the potential for contamination and sample loss through the washing out of "fines" from the long hole rock chip samples by water used in the drilling process.
After discussion with consultant and the author of the latest report, SRK, "it has been agreed that by twinning a number of these long holes with the more reliable "core" drilling method and then comparing and confirming the assay results with nearby long holes, we hope to increase the confidence of the entire long hole data set," the company said in a statement.
If there is a high correlation, this will allow SRK to give the long holes a much wider sphere of influence in a future NI 43-101 resource report, Silver Bull added.
"When we consider that the drills will be starting off underground in high grade silver mineralization, and drilling in an area with a tremendous amount of historical work which already defines this zone we see this as a very low risk program which should add both silver ounces to the deposit, and increase the overall grade within the Shallow Silver Zone," said president and CEO Tim Barry.
The company noted the three goals of the 3,000 metre drilling program are to increase the confidence of the historical long-hole data set, define the extents of the ore body, and infill any gaps that exist in the historical data set.
"This will also be extremely cost effective as we will be using our own drills to do this work and there is very little preparation that needs to be done to the underground workings," added Barry.
The 3,000 metre underground drill program will initially pick 5 or 6 stations within the high grade zone and "twin" the surrounding long holes for a direct assay comparison.
Because much of the high grade zinc resource seen at Sierra Mojada has also been defined with long holes and channel samples, this same approach of twinning selected long holes will eventually be applied to the high grade zinc mineralization at the site - which sits next to and immediately below the Shallow Silver Zone, Silver Bull said.
The Shallow Silver Zone is an oxide silver deposit hosted along an east-west trending fracture-karst system set in a cretaceous limestone-dolomite sequence.
The mineralized body averages between 30 to 120 metres thick, up to 200 metres wide and has 3.688 million tonnes of measured silver mineralization at an average grade of 57 g/t, 45.175 million tonnes of indicated silver with an average grade of 45 g/t, and 8.162 million tonnes of inferred silver with an average grade of 40 g/t, all at a 15 g/t cutoff.
The zone, which remains open to the east and west, has a 3.8 kilometre strike length, of which roughly 60 per cent is at or near surface.
A significant zinc oxide body of 997 million pounds of zinc in the measured and indicated category, and 108 million pounds of zinc in the inferred category lies just next to, and directly underneath the silver mineralization.
There is also an exploration zinc extension target estimated at between 4 to 6 million tonnes grading between 8 to 8.4 per cent, at the eastern end of the zinc mineralization.
The exploration target has been defined by historical data containing 3,733 channels and 1,045 long holes and comprises 70 per cent of the data within these zinc zones, but has too few drill holes to delineate a mineral resource.
Silver Bull is also continuing with its metallurgical program at the project, as well as with mapping and prospecting a number of the Dormidos and Palomas Negros targets.
"In light of the current difficult market conditions and the low cost of the underground program, management has decided to suspend its surface drilling program for the moment," the company concluded.
This drilling had been targeting the extensions of the Shallow Silver Zone to the west and the north as well as a number of near resource exploration targets.
Silver Bull's flagship Sierra Mojada project is located 150 kilometers north of the city of Torreon in Coahuila, Mexico. The company also owns three mineral exploration licenses in Gabon, Africa, two of which are currently under joint venture with AngloGold Ashanti (NYSE:AU).
These licenses are prospective for gold, manganese, and iron ore.