Mexico Silver Deposits

Mexican Silver-Zinc-Lead Belt

The Central Mineral Belt of Mexico hosts most of the major silver-zinc-lead producers of Mexico. Mexico produced 104 million ounces of silver in 2008 making it one of three largest silver producers along with Peru and China. Most of these deposits have very similar characteristics and are classified as Carbonate Replacement Deposits ("CRD"). The similarity of many attributes of these deposits forms the basis of successful exploration models.

For a larger map, please click here for a PDF copy

Although these deposits are well known for their high silver contents they are an important source of zinc and lead with Mexico. The deposits vary from small high grade deposits of less than 1 million tonnes to district size deposits with aggregate of more than 50 million tonnes of ore. In a 1988 summary, Megaw, Ruiz and Titley noted 17 districts of which 8 had reserves or production exceeding 10 million tonnes with average ore grades of 80 to 350 gpt silver and significant zinc and lead production.

The Vinata Project being acquired by Selwyn is located midway between the very large Santa Eulalia and Naica CRD deposits. As illustrated in the tonnage grade graphs they are some of the largest CRD deposits in North America.

Many of the deposits share a common geological setting with the ores hosted by limestones that are overlain by Tertiary volcanic rocks and intruded by mid-Tertiary plutonic rocks. In many of the mines, the Tertiary volcanic rocks form a cap rock that covers the underlying mineralization. The alterations systems consisting of clay alteration and manganese-iron-silver mineralization in these cap rocks are an accepted guide to exploration for the deeper silver-zinc-lead ores. This is readily observed at Santa Eulalia and is a key to exploration at Vinata where all of these features are well developed.

The deposits consist of massive sulphide mantos, chimneys and skarn deposits with the former commonly in the upper part of the system and the later at depth adjacent to intrusive dykes and sills. In other districts silver-gold- base metal vein deposits appear related to similar mineralizing events. In a fully developed mineralized system the various ore conformable and crosscutting lenses occur over a vertical distance of up to 1,000 metres, and commonly occur over several kilometers laterally within the district scale deposits. Deposits such as Santa Eulalia and Fresnillo contain in excess of 500 million ounces of silver and therefore represent very attractive exploration targets.

Ongoing exploration around the known deposits continue to provide significant new discoveries; particularly in covered areas wherein there was no known mineralization. A recent example of this are the attractive vein discoveries made by MAG Silver adjacent to the Fresnillo mine, Mexico’s largest silver producer with 2008 production of approximately 34 million ounces.

Modern exploration utilizing exploration models based on the understanding of stratigraphic and structural controls, and utilizing geophysical techniques and application of alteration and metal zoning models, provides new exploration opportunities within one of the world’s great silver-zinc-lead mineral belts. Selwyn sees these targets as important and an attractive opportunity for discovery and creating value for Selwyn shareholders.