A concerted underground drilling campaign by Scorpio Mining (SPM-T, SMNPF-O) is showing likely expansion of the resource at the Nuestra Seora zinc-lead-silver deposit in northern Sinaloa state, Mexico.
New results from the 8th and 9th levels of the formerly producing mine yielded a number of long high-grade intersections, which the company believes will turn out to be amenable to underground bulk mining.
From the 8th level (260 metres above sea level, and 105 metres vertically below the level of the Nuestra Seora portal), Scorpio has tested both the main Nuestra Seora deposit, and a new discovery dubbed the South Lens. Four holes on the main deposit intersected multiple zones of zinc-lead-silver mineralization, with accessory copper and gold, with drilled widths ranging from 1 to 9 metres, and locally swelling to as much as 18 metres.
In those zones, the wider intersections tended to be among the higher-grade ones too, with a 15.2-metre interval — one of seven in hole NS8L06-48 — grading 8.26% zinc, 4.9% lead, 1.18% copper, 321 grams silver and 0.38 gram gold per tonne. Similarly, a 9-metre interval ran 4.53% zinc, 1.75% lead, 0.73% copper, 136 grams silver and 0.15 gram gold per tonne.
Three holes drilled into the new South Lens target all intersected two or three mineralized intervals, some showing very high grades. A 5-metre interval in hole NS8L06-43 graded 9.91% zinc, 8.64% lead, 6.54% copper, 1,488 grams silver and 0.77 gram gold per tonne.
On the 9th level, 30 metres below the 8th, Scorpio has drilled 34 mineralized holes in its recent program, all into the main deposit. Those included NS9L06-15, which tested downdip from one of the 8th-level holes and cut 11 separate mineralized intersections, making up 24 mineralized metres out of a total length of 92 metres. Zinc grades were mainly in the 1% to 5% range, but a 2-metre interval ran 10% zinc, 2.15% lead, 1.81% copper, 325 grams silver and 0.14 gram gold per tonne, and a 4.8-metre interval averaged 11.44% zinc, 4.5% lead, 3.48% copper, 884 grams silver and 0.23 gram gold.
Most of the holes from the 9th level returned zinc grades of 1% to 5%, lead grades from 0.5% to 3%, and silver grades between 100 and 400 grams per tonne, with local higher-grade results often correlated with wider mineralized structures. In general, the mineralized widths were comparable to those intersected from the 8th level.
A January resource estimate on Nuestra Seora put the size of the measured and indicated resource at 3.5 million tonnes, averaging 2.27% zinc, 1.06% lead, 0.38% copper, 118 grams silver and 0.15 gram gold per tonne. Another 4.1 million tonnes falls into the inferred category, with grades of 2.18% zinc, 1% lead, 0.22% copper, 132 grams silver and 0.19 gram gold per tonne. The company expects a significant increase in that resource out of the recent underground drilling.
Geotechnical studies in the Nuestra Seora zones have concluded stopes 60 metres high, and 25 by 30 metres in horizontal dimension, would be stable without needing support. Those ground conditions are favourable for underground open stoping methods.
Metallurgical tests on the Nuestra Seora mineralization late last year showed that three concentrates — lead, zinc and copper — could be produced, with 92% of the lead recovered to the lead concentrate, 88% of the zinc recovered in the zinc concentrate, and copper distributed between all three. Work continues on more effective separation of the copper.
In June and again in October of last year, Scorpio announced it had discovered new mineralized zones at Nuestra Senora. Those two zones, Hoag and September 9, have both provided significant drill intersections since their discovery.
Recent infill drilling on the Hoag zone intersected mineralization in seven holes, with typical drilled lengths in the 13 to 25-metre range. The intersections mainly ran 1% to 3% zinc, with lead grades about the same, plus 38 to 184 grams silver per tonne and credits in copper and gold. Initial metallurgical tests on the Hoag mineralization showed lead recoveries of 93% to a lead concentrate, zinc recovery of 71% to a zinc concentrate, and copper recoveries of 88% to three concentrates, lead, zinc and copper. Silver mainly reported to the lead concentrate, with about 78% recovery, and another 8% reported to the two other concentrates.
Scorpio expects to have the results of a prefeasibility study some time in April or May. In preparation for development, and to facilitate exploration work, a 34-km power transmission line should be complete in July.
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