"Sierra Mojada is one of only a handful of projects with any appreciable zinc resources and is one of the largest undeveloped silver-zinc projects in Mexico," Silver Bull president, CEO and director Tim Barry said.

Silver Bull said it had wanted to recalibrate the resource to the current price environment, given the movements since the 2015 resource, resulting in a significant increase in the zinc resource and a slight decrease in silver.

It used a zinc price of US$1.20/lb and $15/oz for silver, rather than the $1/lb and $18/oz used previously.

Zinc had hit a 10-year high above $3,606/t early this year but has since retreated to about $2,552/t, while silver has slid about $3 this year to around $14.30/oz on the spot market today.

The update takes the project's total measured and indicated resource to 70.4 million tonnes at 38.6g/t silver and 3.4% zinc, for 87.4 million ounces of silver and 5.3 billion pounds of zinc.

This compares with a previous 56.8Mt at 50g/t silver and 3.4% zinc for 90.8Moz of silver and 4.3Blb of zinc, the company said.

The resource now also contains two "separate and distinct" openpittable, measured and indicated high-grade zones.

The zinc zone comprises 13.5Mt at 11.2% zinc for 3.3Blb, using a 6% cut-off.

The silver zone of 15.2Mt at 114.9g/t contains 56.3Moz at a 50g/t cut-off.

Barry said the project provided excellent leverage to both zinc and silver prices and had the potential to be scaled in size depending on metal prices.

Silver Bull shares have been on a downward trend since January's high of C29c, but they rose more than 30% yesterday to 15c, capitalising it at $35.2 million.