Hoping to add new life to an old producer, Calgary-based junior Stratabound Minerals (SB-A) continues to explore its Sierra Azul lead-zinc-silver property in Mexico’s Coahuila state.
Situated 50 km south of the industrial city of Monclova, Sierra Azul is accessible by paved highway and gravel road. A major railroad, 220-kV power line and several lead-zinc smelters are also nearby.
Small-scale mining at Sierra Azul dates back to the 1800s, when rich near-surface oxide material, reportedly running better than 30% combined lead-zinc, was exploited in what is now known as the Santa Genoveva deposit.
The operation was converted to an underground mine in the 1970s, however, after massive-sulphide mineralization was discovered in the lowermost workings, about 30 metres below the access level. Following the discovery, a total of 4,000 tonnes averaging 12% zinc, 4% lead, 30.9 grams silver and 0.25 gram gold per tonne was mined.
Activity waned in 1977, and the project fell into obscurity for the next two decades, during which time it changed ownership twice through inheritance.
Legal considerations prohibited the beneficiaries from seeking assistance from outside parties until early last year, when Stratabound struck a deal with the owners.
“Like many other Canadians, we were initially looking for gold,” said Stratabound President Stan Stricker. “While there were many such opportunities, none offered the prospect for immediate exploration success with the same degree of probability as this property.”
Stratabound can earn a 100% interest in the 63-ha Sierra Azul property by making annual payments of US$125,000 over five years. If the mine is revived, the deal also becomes subject to a 1% net smelter return royalty, although Stratabound can buy it out at any time for US$500,000, minus the option payments. Shortly after closing the deal, the company also staked ground along strike from, and adjacent to, the Santa Genoveva deposit, thereby increasing the property’s size to its current 18.8 sq. km.
Geologically, Sierra Azul covers 10 km of a northwest-southeast-striking carbonate sequence. In addition to hosting Santa Genoveva, the sequence also contains several other smaller areas of mineralization, several of which are sites of historical workings. The deposit itself is hosted by a brecciated dolomite and an adjacent 15-metre-thick stratiform manto body, which formed at the contact of the dolomite and an arkosic unit. Both bodies owe their existence to replacement-style mineralizing events.
Stratabound initially focused its efforts on the underground workings, mapping and sampling a number of them. A total of 29 individual channel samples were taken along a 190-metre strike length of the breccia unit, with the average for the set reported at 12.2% zinc, 6.9% lead and 13.7 grams silver. As well, seven similar samples were taken from the manto body; they averaged 18.3% zinc, 6.4% lead and 16.6 grams silver. Four 16.5-metre-long samples taken across a 175-metre-long waste dump averaged 7.5% zinc, 6.2% lead and 11 grams silver.
Surface exploration elsewhere on the property has also borne fruit, especially along strike of the deposit. About 1.3 km northwest of the deposit, samples from one mineralized outcropping ran as high as 14% zinc, 1.4% lead and 2 grams silver. In the opposite direction, a number of samples from five collapsed workings situated 1 km southeast of the mine returned values of up to 8.3% zinc, 2.6% lead and 42.2 grams silver. The workings, which occur in the same breccia unit that hosts the Santa Genoveva deposit, bring the total length of mineralization traced on surface to 4.1 km.
Potentially more significant are the results obtained from a recently completed induced-polarization (IP) survey. The survey outlined two chargeability anomalies coinciding with the surface trace of mineralization and a separate, parallel anomaly to the southwest.
“The geophysics and the geology fit together perfectly,” said Stricker.
The first chargeability anomaly, which coincides with the Santa Genoveva deposit, was traced for 500 metres, after which it is believed to dip below the 125-metre detection range of the geophysical equipment. The chargeable body varies in width between 50 and 600 metres, and is believed to reflect sulphide mineralization that grades into an oxide zone at shallower depths.
The second anomaly is also interpreted as a zone of sulphide mineralization, however, it is described as having nine times the intensity of the first. It begins 300 metres southeast of the first anomaly and continues for another 800 metres in that direction, ending at the southeasternmost workings mapped on surface. The anomaly increases from a width of 50 metres at its northwestern end to 250 metres near the middle, or 500 metres if a weaker adjacent feature is included.
Stratabound notes that both chargeable bodies occur within a continuous zone of low resistivity. This, says Stricker, is a reflection of the favorable dolomite breccia unit.
A third parallel chargeability anomaly was also detected, but it is being treated as a secondary target. The anomaly starts 600 metres southwest of the known mineralized trend and varies in width from 150 to 550 metres along its 1.9-km length.
Stratabound is currently focusing on the smallest anomaly (associated with Santa Genoveva), where a number of drill holes are planned. Only one hole has been completed so far, and although full results are pending, several wide zones of oxide mineralization are reported to have been intersected.
Several other drill holes are also planned for the stronger geophysical anomaly to the southeast. In all, 3,000 metres will be drilled from surface, after which an underground drill program will begin.
Stratabound is also completing its interpretation of the remaining geophysical data collected from that portion of the survey covering mineralization to the northwest of the first anomaly. Results are expected to be released shortly.
Meanwhile, Consolidated Magna Ventures (CMV-V), which is also targeting replacement-style polymetallic deposits in northern Mexico, recently began a program of geophysical surveying on its Koala property in Chihuahua state.
Magna’s program will focus on extending a 2.6-km-long chargeability anomaly that was outlined in a previous program. The anomaly is coincident with a 3.5-km-long by 500-metre-wide zone of altered limestone that is believed to have potential for lead, zinc, silver and copper mineralization.
Current work is focused on the southeastern end of the chargeable body, where a gradient IP survey is attempting to extend the anomaly.
Reconnaissance IP surveys are also planned along trend to the southeast and northwest, and gravity and dipole-dipole IP surveys are planned for selected areas of the anomaly that may correlate with massive sulphide mineralization.
Dipole-dipole surveys provide higher resolutions than gradient surveys.
A 2,000-metre drill program will begin by May. The program will test a minimum of four targets outlined by the geophysical work.
The Koala property covers 12,765 ha and is divided into three claim blocks, dubbed Koala I, Koala II and Koala III. A minimum of $500,000 will be spent in the current program, with the funds to be provided by NovaGold Resources (NRI-T) as part of its US$3-million commitment to earn a 51% interest in Koala II and III and 51% of Magna’s option to earn 95% in Koala I.