VANCOUVER – Eight months, 16,700 metres of drilling, and 400 channel samples later, Silver Bull Resources (SVB-T) has doubled the silver resource at its Sierra Mojada project in Coahuila, Mexico.
Mineralization at Sierra Mojada is associated with the Sierra Mojada fault. The known zone extends for more than 6 km and contains two distinct targets. Silver Bull's main focus is the Shallow Silver zone, which is a near-surface occurrence of silver oxide mineralization. The silver originally existed as sulphide mineralization but was remobilized and reconstituted as a manto-style oxide deposit.
That manto is now home to a defined resource of 71.9 million indicated tonnes grading 72.5 grams silver per tonne and 1.38% zinc, for a contained metal count of 167.5 million oz. silver and 2.19 billion lbs. zinc.
Those same 71.9 million tonnes of resource also host lead and copper mineralization at average grades of 0.34% lead and 0.08% copper. However, since the geologic constraints and metallurgical responses of those elements are not as well understood as those on the silver and zinc, the lead and copper grades are classified as inferred.
The updated resource represents a 103% increase in contained silver compared to the last estimate, which Silver Bull released in July 2012.
"At over 167 million ounces, Sierra Mojada is now one of the largest undeveloped silver resources in Mexico," said Silver Bull president and CEO Tim Barry in a statement. "It is also no small point to note that even though we have defined a much larger resource than previously reported, mineralization remains open on the deposit."
Silver Bull has tracked the manto for 3.8 km along strike and found it to average 200 metres in width and 140 metres in thickness. More than half of the deposit delineated to date is at or very near surface; at the eastern end it starts to dip gently to the east. The deposit is classified as a carbonate replacement deposit, though an intrusive source has yet to be located.
The other target at Sierra Mojada lies beneath and east of the Shallow Silver. It is the Zinc zone, a high-grade zinc exploration target that strikes for 1.5 km. Results to date indicate the zone carries a zinc grade of 8% or better, though it has not yet been subjected to a comprehensive resource estimate.
Silver Bull has been busy since it last estimated the resource within the Shallow Silver zone. Since the middle of last year the company has completed 10,000 metres of surface diamond drilling, 6,650 metres of underground diamond drilling, and approximately 400 channel samples. The underground drilling program was designed to twin historic long holes and the effort met with great success, enabling Silver Bull to utilize more than 40,000 metres worth of historic underground drill data much more extensively than was possible before the data were validated.
History abounds at Sierra Mojada. Silver and lead were first discovered in the area in 1879. For the next hundred-plus years zinc, silver, and lead ores were mined from various spots along the fault, including within what is now the Sierra Mojada property. In fact, there are more than 50 historical mine shafts are scattered along the east-west zone, many reaching more than 200 metres into the ground. Ores extracted from these shafts were generally hand sorted and the high-grade selection shipped to smelters in the United States.
Silver Bull has been at work at Sierra Mojada for some time. In 1996 the company, known then as Metalline Mining, signed an agreement to earn into Sierra Mojada. By 2000 the company acquired full ownership of the site. The next year Peñoles signed on as a joint venture partner. The Mexican mining major completed an underground exploration program including new underground raises as well as diamond and percussion drilling before walking away from the project in 2003.
In 2010 Metalline Mining merged with Dome Ventures, retaining the Metalline name until April 2011 when it changed its name to Silver Bull Resources.
Sierra Mojada is accessible by paved roads from the city of Torreon, which lies about 250 km to the southwest. Most of the lands around the project are used for cattle ranching, though the southeastern project border abuts a dolomite extraction and processing facility that has its own rail line.
In February Silver Bull closed a financing, raising US$9.2 million by selling 22.9 million units at US40¢ a piece. Each unit comprised a share and half a warrant, with each warrant exercisable at US55¢ for 18 months. The raise provided Silver Bull with sufficient funds to complete the resource estimate, continue drilling, and embark on a preliminary economic assessment at Sierra Mojada.
Silver Bull's share price gained 1.5¢ on news of the new Sierra Mojada resource to close at 38¢. The company has a 52-week trading range of 31¢ to 60¢ and has 159 million shares outstanding, 180 million fully diluted.
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