Silver Bull Resources (TSE:SVB)(NYSE MKT:SVBL) reported Wednesday what it called "exceptional" preliminary metallurgical results on the silver and zinc mineralization at its Sierra Mojada project in northern Mexico.
The company released a series of bottle roll tests on the silver mineralization from the Centenario zone, which represents about one third of the silver at Sierra Mojada, as well as pyro-metallurgical tests using a rotary kiln from the Red Zinc zone.
The silver and zinc explorer said today that silver recoveries from the Centenario zone were up to 89 per cent, with an average recovery of 83 per cent silver across a variety of silver grade ranges. Silver recoveries generally showed an increase with higher grades.
The highest silver recoveries were achieved at a 75 micron grind, Silver Bull said, using a cyanide strength of 5 grams per liter over a 24-hour time period. Work was focused on cyanide leach recovery of the silver using "bottle roll" tests to simulate an agitation leach system common on many mine sites, the miner added.
Meanwhile, roasting of the Red Zinc ore achieved up to 98.9 per cent removal of zinc from the ore via fuming - producing an almost pure zinc oxide concentrate of 80 per cent, at a 1,300 degree Celsius roasting temperature.
Test work on the Red Zinc zone was completed from channel samples along the 1.5 kilometre strike length of the target, with initial tests focused on roasting the ore in a rotary kiln to fume off the zinc and collect it as a zinc oxide concentrate. The company said zinc fuming shows "an obvious increase" in recovery with increasing temperature.
"We are extremely pleased with these preliminary metallurgical test results for the silver and zinc mineralization," said president and CEO, Tim Barry.
"When we consider silver oxide deposits often have recoveries in the low 60% range, the results we see in the Centenario zone are exceptional.
"We are also very pleased that we have been able to achieve the +90% fuming of the zinc that we see with the Waelz kilning technique already used in the industry. This, combined with the fact that we have a functioning railway right to site is a serious positive for the "mineability" of the zinc at Sierra Mojada."
Barry went on to state that the company's goal is to put out a new resource update and have a viable flow sheet in place before the end of the first quarter of 2013, after which it will look to take the project to next level through a preliminary economic assessment.
The Centenario zone is hosted along a buried east-west trending structure which lies parallel and 300 metres to the north of the "Sierra Mojada" fault - which hosts the Shallow Silver and Fonteriza zones.
As well as continuing tests to assess silver recoveries through cyanidation, the company said studies are also planned to see if another process can be applied at the back end of the leaching circuit to potentially lower cyanide costs, as well as recover a portion of the zinc and copper also seen in the ore.
Silver results are expected from bottle roll tests on the "Shallow Silver" and "Fonteriza" zones shortly. Once the preliminary program is complete, work will then move to focus on optimizing recovery, looking at parameters such as head grade of the silver ore, grind size, and cyanide concentration.
The roasting of the zinc ore, meanwhile, aims to simulate a "Waelz Kiln", Silver Bull said, which is a kiln used to recycle zinc from steel dust and regularly achieves recoveries in excess of 90 per cent.
In using this process, the zinc resource at the project would benefit, as the property lies in the state of Coahuila - the largest coal producing state in Mexico - which would provide the fuel to run the kiln. The project also has a functioning railway right to site to allow for easy transport of coal, and of the zinc concentrate from the asset.
Pyro-metallurgical tests are ongoing for zinc, and a series of larger sample sizes will now be used to replicate the initial bench top results. In addition to these tests, Silver Bull also has a full program underway to assess hydro-metallurgical recovery potential on the zinc.
Over the past months, Silver Bull has been consistently releasing high grade silver results from Sierra Mojada, from its program designed to twin a series of what the company calls "long holes" in a high grade silver zone found at the eastern end of the Shallow Silver zone at the property.
The aim of the campaign is to increase confidence in the historical long hole data set, which represents 38,000 metres of drilling that was either "severely restricted" or discarded in the company's latest NI 43-101 resource report on the Shallow Silver zone in July.
The latest batch of high grade silver results included 15.05 metres of at 463.55 grams per tonne (g/t) silver, including 3.1 metres at 1,654.92 g/t silver in hole T12090.
The company's 3,000 metre drill program in the high grade silver zone is ongoing, with two underground rigs. As the silver and zinc miner said in September, it has expanded the underground drill program with an additional 2,000 metres to twin a series of long holes in the high grade zinc zone, which sits just below the silver mineralization.
The twinning drill program is slated to wrap up before the end of the year, Silver Bull said, after which it will initiate a revised NI 43-101 resource update on the Shallow Silver and Zinc zones, scheduled for release in the first quarter of 2013.
At a 20g/t cutoff grade, the Shallow Silver Zone has a measured resource of 3.023 million tonnes at an average grade of 65 g/t for 6.343 million contained troy ounces of silver, an indicated resource of 38.560 million tonnes at an average grade of 50 g/t for 61.694 million contained troy ounces of silver, and an inferred resource of 6.491 million tonnes at an average grade of 45 g/t for 9.478 million contained troy ounces of silver.
Silver Bull's main Sierra Mojada project is located 150 kilometres north of the city of Torreon in Coahuila, Mexico, while the company also has 2 mineral licenses in Gabon, Central Africa, which are prospective for gold, manganese, and iron ore.
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