Corner Bay tests Alamo Dorado extensions

Having replenished its till, Corner Bay Minerals (bay-t) is again drilling its already sizable Alamo Dorado silver-gold deposit in Mexico’s Sonora state.

Alamo Dorado hosts an independently measured resource of 74.8 million tonnes grading 41 grams silver and 0.16 gram gold per tonne. Within that resource is a higher-grade, nearer-surface pocket containing 4.2 million tonnes at 130 grams silver and 0.32 gram gold.

Corner Bay recently raised $1.2 million by issuing 400,000 shares priced at $3 apiece. Each share comes with a half-warrant attached, with a full warrant entitling the holder to buy an additional share within two years at $4 each. Proceeds are earmarked for Alamo Dorado.

The current, 10,000-metre campaign is testing for extensions downdip and northwest of the known resource. This drilling will extend several earlier holes that bottomed in high-grade silver and gold mineralization, at the footwall contact of the epithermal system.

To the northwest, several holes will follow up on two earlier holes that cut long but low-grade alteration. Corner Bay says subsequent structural mapping at surface has since provided a clearer picture of the controls on mineralization. Although the area is offset considerably to the west, it is considered to be the deposit’s northwestern strike extension.

A third, less-explored area lies southeast of the deposit, on the slope of an adjacent ridge. Here, several holes will test a geochemical anomaly measuring 700 metres long by 100 metres wide, similar to the surface dimensions of Alamo Dorado.

Corner Bay began the Alamo Dorado project in September 1997, after optioning 503 ha from local vendors for US$800,000, payable over six years. Impressive preliminary results (63 metres grading 47 grams silver and 0.35 gram gold) prompted the company to stake 4,865 ha of surrounding ground to cover any possible strike extensions.

To date, 42 reverse-circulation (RC) holes totalling 9,854 metres have defined the deposit over a northwesterly strike length of 600 metres. Mineralization dips to the west, sub-parallel to the western slope of the ridge that encloses it, making low-cost open-pit mining a strong possibility. (Preliminary studies by Arizona-based Mintec, which calculated the resource, suggest stripping ratios as low as 0.4-to-1.)

Geologically, Alamo Dorado lies on the western flank of the Sierra Madre Occidental geological province. Both silver and gold occur predominantly as free particles disseminated in the host gneisses and schists. Silver is also tied up in secondary oxide minerals, particularly chlorargyrite, a soluble chloride mineral found in secondary enrichment zones above silver veins subjected to intense weathering.

Weathering has oxidized the deposit down to at least 250 metres below surface. Argillic alteration is also prevalent down to that depth.

Early indications of the metallurgical characteristics of the deposit are said to be encouraging. Preliminary tests by Metcon of Arizona suggest recoveries of 90% for gold and 89% for silver.

Metcon is currently studying optimal crush sizes and solution flow rates on composite samples of four large-diameter core holes drilled last fall. Each of the holes was drilled to between 275 and 290 metres below surface, in the middle of the deposit, between earlier RC holes. Results include:

– 230 metres of 110.5 grams silver and 0.23 gram gold in hole 1;

– 203 metres of 74 grams silver and 0.25 gram gold in hole 2;

– 184 metres of 44 grams silver and 0.18 gram gold in hole 3; and

– 168 metres of 74 grams silver 0.2 gram gold in hole 4.

The tests are expected to take several months to complete.