Mining Intelligence and News
United States

Shafter Mine

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Mine TypeUnderground
  • Silver
Mining Method
  • Room-and-pillar
  • Bench stoping
Mine Life... Lock
SnapshotThe Shafter silver mine has all material permits in place with extensive surface infrastructure and underground workings including portal/decline and shaft access and a processing facility rated at approximately 1,500 tons per day. Mining was discontinued after the plant commissioning and testing phase were complete, due mostly in part to lower silver prices and rushed production start-up issues. The mine was put on care and maintenance in December 2013.


Aurcana Silver Corp. 100 % Indirect
Aurcana owns 100% of the Shafter project through its wholly owned subsidiary, Rio Grande Mining Company (“RGMC”).

Silver Hammer Mining Corp. has entered into a definitive share purchase agreement dated September 27, 2023, to acquire a 100% interest in the Shafter silver deposit, a previously producing high-grade silver mine, from Aurcana Silver Corporation.

Completion of the Shafter Acquisition is subject to customary conditions such as shareholder approval, regulatory approvals, completion of the equity financing, the reorganization, the debt settlement, and approval of the CSE.

Deposit type

  • Manto
  • Vein / narrow vein
  • Carbonate hosted


The Shafter silver deposit is considered an example of a polymetallic replacement deposit. Because of their irregular, but sharp contact with the enclosing carbonate host rocks, deposits of this type have been categorized as high-temperature, carbonate-hosted deposits.

Polymetallic deposits consist of massive lenses and (or) pipes, known as mantos or replacement orebodies, and veins of iron, lead, zinc, and copper sulfide minerals that are hosted by and replace limestone, dolomite, or other sedimentary rocks; most massive deposits contains more than 50 percent sulfide minerals. Sediment-hosted deposits commonly are intimately associated with igneous intrusions in the sedimentary rocks. Emplacement of these intrusions triggered mineral formation and they host polymetallic veins and disseminations that contain iron, lead, zinc, and copper sulfide minerals. Some polymetallic replacement deposits are associated with skarn deposits in which host carbonate rocks are replaced by calc-silicate±iron oxide mineral assemblages. Most polymetallic vein and replacement deposits are zoned such that copper-gold mineralization is proximal to intrusions, whereas lead-zinc-silver mineralization is laterally and vertically distal to intrusions.

There is little evidence in the Shafter district to indicate the source of the mineralizing solutions. No evidence of contact metamorphism has been noted, and this may indicate that the mineralizing solutions had traveled some distance, either horizontally or vertically through the stratigraphy.

The Shafter deposit is hosted within the gently dipping beds of the Permian Mina Grande Formation, just below their contact with Cretaceous rocks. The reef-derived dolomite and limestone of the Mina Grande Formation were susceptible to differential weathering and karst activity at the upper level of the formation, and passageways for mineralizing solutions formed along facies contacts and bedding planes.

The deposit is parallel to the bedding, has a tabular form, and is called a manto deposit, following colonial Spanish terminology for a blanket-like or tabular mineralized body. The deposit has some irregularities in its shape but dips generally east. Veins containing the same minerals as the manto are common in the eastern part of the Shafter district. Many of these veins are fissure fillings and have brecciated zones. Rozelle (2001) stated that the mineralization took place after the intrusion of dikes and sills of Tertiary age, and Ross (1943) reported that dikes in the Presidio mine are somewhat mineralized.

Mineral deposition took place in four main phases: (1) a limited amount of dolomitization; (2) silicification; (3) deposition of calcite and metallic minerals including galena, sphalerite, and acanthite; and (4) supergene alteration. Aurcana identified two separate stages of metal mineralization on the Shafter property – an initial lead stage potentially associated with the north-trending Mina Grande fault, followed by a second stage consisting of silver and anomalous lead and zinc, thought to be associated with the Herculano fault system and multiple east-trending faults that served as distal feeder systems (Lambeck, 2012). Contacts of the mineralized zones with unaltered wall rocks are generally sharp.

Silver mineralization located to the east of the Presidio mine historical workings (designated Block Groups I and II in the historical reports and re-named the Shafter area for use in this report) appears to be continuous within the manto deposit, which extends over 6,000ft of strike length along a zone trending roughly N60°E and lies between 700 and 900ft below the surface. The entire Presidio/Shafter deposit is up to 1,500ft wide in a north-south direction and extends at least 2.5 miles on an east-west trend (Balfour Holdings, Inc., 2000). There appears to be a high-grade core within the broader mineralized zone located just below the Cretaceous-Permian unconformity. The high-grade core is very continuous east of the Presidio mine workings in the Shafter area and in the upper workings of the Presidio mine (Balfour Holdings, Inc., 2000).

About 5,000ft northeast of the eastern limit of stoping in the Presidio mine, silver values decrease markedly. About 1,000ft further east, the favorable Basal and Pseudobreccia units of the Mina Grande Formation were removed by pre-Cretaceous erosion or dolomitization (Kastelic, 1983). West of the Presidio mine, dolomitization has also destroyed much of the favorable host rock for the Shafter-type mineralization (Kastelic, 1983).

The mineralized material consists of a massive aggregate of medium-grained, vuggy silica stained with varying amounts of iron and manganese oxides. Mineralogy is fairly consistent within the district. The mineralization originally consisted of sulfide minerals, which are now almost thoroughly oxidized. Secondary minerals include iron and manganese oxides, acanthite, hemimorphite, descloizite, embolite, plumbojarosite, cerargyrite, native silver, cerussite, anglesite, and small amounts of covellite, chrysocolla, and possibly other copper minerals. Primary minerals include dolomite, calcite, quartz, pyrite, sphalerite, galena, argentite, chalcopyrite, covellite, molybdenite, and tetrahedrite. Silver occurs predominately as oxidized acanthite in fine-grained aggregates of quartz, calcite, and goethite, with lesser dolomite, hemimorphite, willemite, anglesite, galena, smithsonite, and sphalerite. Lead and perhaps zinc appeared to be more plentiful relative to silver in the outlying mines of the district than in the Presidio mine, although the outlying mines are scattered and were poorly developed so generalizations are difficult (Ross, 1943).

Mineralization occurs over a 13,000 ft east-northeast strike length, is up to 1,200 ft across, and is generally 10 to 20 ft thick. The resource is at a depth of less than 100 ft in the west-central portion of the deposit and then gradually deepens to a depth of more than 1,000 ft within the eastern end of the deposit following the general stratigraphic dip. Manto thickness and silver grades can be highly variable, often related to near-vertical structures that served as fluid conduits and/or structural traps.

Although silver mineralization is generally continuous along the 13,000 ft length of the deposit, the resource is fragmentary in the vicinity of the historic Presidio mine due to the removal of mined-out material, as well of west of the historic Presidio mine in the area more recently mined by Aurcana.



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CommodityUnitsDailyAvg. AnnualLOM
Silver koz 5.31,8376,559
All production numbers are expressed as metal in doré.

Operational metrics

Daily ore mining rate 600 tons *
Daily processing rate 600 tons *
Hourly processing rate 25 tons *
Annual ore mining rate 210,000 tons *
Annual processing rate 210,000 tons *
Waste tonnes, LOM 228.7 k tons *
Ore tonnes mined, LOM 748.7 k tons *
Total tonnes mined, LOM 977.3 k tons *
Tonnes processed, LOM 749,000 tons *
* According to 2018 study.

Production Costs

Cash costs Silver USD 10.4 / oz *  
Assumed price Silver USD 18.5 / oz *  
* According to 2018 study / presentation.

Operating Costs

UG mining costs ($/t milled) USD 51.5 *  
Processing costs ($/t milled) USD  ....  Subscribe
G&A ($/t milled) USD  ....  Subscribe
Total operating costs ($/t milled) USD  ....  Subscribe
* According to 2018 study.

Project Costs

MetricsUnitsLOM Total
Pre-Production capital costs $M USD  ......  Subscribe
Total CapEx $M USD  ......  Subscribe
UG OpEx $M USD  ......  Subscribe
Processing OpEx $M USD 16.8
G&A costs $M USD 6.5
Total OpEx $M USD  ......  Subscribe
Mining Taxes $M USD  ......  Subscribe
Income Taxes $M USD  ......  Subscribe
Royalty payments $M USD  ......  Subscribe
Gross revenue (LOM) $M USD  ......  Subscribe
Net revenue (LOM) $M USD  ......  Subscribe
Pre-tax Cash Flow (LOM) $M USD  ......  Subscribe
After-tax Cash Flow (LOM) $M USD  ......  Subscribe
Pre-tax NPV @ 5% $M USD  ......  Subscribe
After-tax NPV @ 5% $M USD  ......  Subscribe
Pre-tax IRR, %  ......  Subscribe
After-tax IRR, %  ......  Subscribe
Pre-tax payback period, years  ......  Subscribe
After-tax payback period, years  ......  Subscribe

Required Heavy Mobile Equipment


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Mine Management

Job TitleNameProfileRef. Date
....................... Subscription required ....................... Subscription required Subscription required Dec 15, 2023
....................... Subscription required ....................... Subscription required Subscription required Dec 15, 2023

Total WorkforceYear
...... Subscription required 2018

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