The Copalquin District Mining Concessions, Mexico

November 2021

  • A maiden JORC indicated and inferred mineral resource has been estimated for the first drill target area of El Refugio–La Soledad in the Copalquin District, Mexico.
  • 2,416,000 tonnes @ 4.80 g/t gold, 141 g/t silver for 373,000 oz gold plus 10,953,000 oz silver (Total 529,000 oz AuEq*) using a cut-off grade of 2.0 g/t AuEq*
  • 28.6% of the resource tonnage is classified as indicated
  • Copalquin is a district scale opportunity with El Refugio-La Soledad one of several drill targets
  • Drilling is continuing at El Refugio–La Soledad including along strike from the recently announced hole CDH-094 with 18.67m @ 9.64 g/t gold, 278.8 g/t silver (5 Nov. 2021)
  Tonnes (kt) Gold (g/t) Silver (g/t) Gold Equiv.* (koz) Gold (koz) Silver (koz)

Gold Equiv. * (koz)

El Refugio Indicated 691 5.43 114.2 7.06 121 2538 157
Inferred 1447 4.63 137.1 6.59 215 6377 307
La Soledad Indicated - - - - - - -
Inferred 278 4.12 228.2 7.38 37 2037 66
Total Indicated 691 5.43 114.2 7.06 121 2538 157
Inferred 1725 4.55 151.7 6.72 252 8414 372
TOTAL 2416 4.8 141 6.81 373 10953 529

Table 1 – Mineral resource estimate El Refugio – La Soledad using a cut-off grade of 2.0 g/t AuEq*

Copalquin District – Maiden Mineral Resource Estimate (16 November 2021) by AMC Consultants

View Mineral Resource Estimate

*AuEq. = gold equivalent calculated using and gold:silver price ratio of 70:1. That is, 70 g/t silver = 1 g/t gold. The metal prices used to determine the 70:1 ratio are the cumulative average prices for 2021: gold USD1,798.34 and silver: USD25.32 (actual is 71:1) from kitco.com

Figure 1 – Mining concession area covering the Copalquin Mining District with Maiden MRE (November 2021) for the first target area. Main historic mine workings shown and areas of expanded exploration to expand the gold and silver resources in the district during the next 12 months.

*AuEq. = gold equivalent calculated using and gold:silver price ratio of 70:1. That is, 70 g/t silver = 1 g/t gold. The metal prices used to determine the 70:1 ratio are the cumulative average prices for 2021: gold USD1,798.34 and silver: USD25.32 (actual is 71:1) from kitco.com

Area: 70km2 (10km E-W by 7km N-S) and includes dozens of historic mines and workings.

Location: Durango State, Mexico, 4 hour drive north of the city of Culiacan and 8 hour drive SSW from the city of Chihuahua via highway 24.

The town of El Durazno is located approximately 20km east of the District. The Copalquin airstrip is serviced several times daily from Tamazula (15 minutes) and Culiacan (30 minutes).

Mithril is currently completing (December 2021) a fully funded drill program in the Copalquin District following its successful maiden drill program completed during the second half of 2020. The near-term goal of a maiden JORC mineral resource estimate (MRE) for the El Refugio-La Soledad area has been achieved in November 2021 with drilling continuing to expand the deposit strike length.

Figure 2 – Copalquin Mining District location map in Durango State, Mexico and other mines and projects within the state.

Exploration Activity in Mexico

Mithril commenced drilling in the district late July 2020 following the 100% acquisition of Sun Minerals Pty Ltd which, via its Mexican subsidiary, has an option to purchase the Copalquin District mining concessions (detailed in ASX announcement dated 25 November 2019).

Mithril has focussed its drilling at the El Refugio discovery area and the adjacent El Cometa and La Soledad mine areas as shown in Figure 1.

At the historic mine area of La Soledad to the north of El Refugio, high-grade gold-silver intercepts have been returned from 15 diamond core drill holes and part of the has been included in the maiden JORC MRE for El Refugio-La Soledad (November 2021).

Figure 3 – Long section from main El Refugio structure to Los Reyes.

Figure 4 – Long section for El Refugio showing the drill hole pierce points. Area highlighted for the Maiden JORC mineral resource estimate November 2021.

*AuEq. = gold equivalent calculated using and gold:silver price ratio of 70:1. That is, 70 g/t silver = 1 g/t gold. The metal prices used to determine the 70:1 ratio are the cumulative average prices for 2021: gold USD1,798.34 and silver: USD25.32 (actual is 71:1) from kitco.com

Preliminary Concept for Mine Access – El Refugio

Deep high-grade intercepts such as in holes CDH-061, CDH-071 and CDH-077 bring mineralisation closer to potential access from a site with favourable logistics, taking advantage of the local topography. The CDH-077 ‘bonanza zone’ can be reached by an exploration drift (adit) of approximately 750 metres long. Such a drift would allow access for the close-spaced sampling that will be necessary to bring the bonanza grade zone into higher confidence resource categories.

Figure 5 – Schematic showing an underground mine access concept for the El Refugio gold-silver deposit, Copalquin District, Mexico

Geology

The Copalquin Project lies within the Sierra Madre Occidental physiographic province of north-western Mexico. The project is underlain by andesitic volcanics of the Cretaceous-Tertiary Lower Volcanic Series. A Tertiary granodiorite to monzonite pluton intrudes the andesite and much of the area is capped by Tertiary rhyolite ignimbrites of the Upper Volcanic Series. Mineralisation is thought to be contemporaneous with the eruption of the Upper Volcanic Series.

Semi-continuous low-angle breccia zones have formed within the andesite parallel to the granodiorite contact. These zones include the El Cometa breccia and the Los Reyes breccia. The geometry of these zones is similar to the nearby El Gallo silver deposit of McEwen Mining which is also formed in a series of breccias parallel to the contact between intrusive rocks and Lower Volcanic Series andesite.

A series of high angle normal faults strikes northwest and dips to the northeast including the Refugio, La Soledad and La Constancia structures which host veins mineralised with gold and silver. North-south striking, west dipping faults at San Manuel also host mineralized veins.

Both the low-angle breccias and the high-angle faults host extensive zones of mineralised quartz breccia. It is likely that the low angle zones developed as tectonic breccias during the intrusion of the granodiorite and were later mineralized by hydrothermal activity related to the eruption of the Upper Volcanic Series.

Large areas of argillic alteration occur across the concessions. The alteration forms haloes adjacent to the known structures and large zones where structures have not been identified. Argillic alteration is indicative of widespread penetration of hydrothermal fluids into the surrounding rocks and suggests a long-lived hydrothermal system was active at Copalquin.

The alteration from Refugio to Los Reyes is over 2,000 meters long and from 100 to 400 meters wide. It is expected that the widest zones are related to shallow-dipping portions of the Cometa-Los Reyes structures where the structure is nearer the outcrop surface. Similar alteration is present well to the west at El Platanal and well to the east at Constancia. It cannot be stressed enough that this strong, widespread argillic alteration forming a large-volume halo well out from the veins is the observable geologic characteristic that identifies Copalquin as a major epithermal centre.

Copalquin Mining District History

  • Discovered in the 1848, production ceased during the Mexican Revolution.
  • El Refugio first mined in 1849. By 1897 there were 10 head stamp batteries installed with cyanidation plants.
  • 1935 the company Minera CIBOLA milled ore from the San Manuel and El Cometa mines.
  • Detailed sampling of some workings by Industrial Mineral Mexico S.A. de C.V. (IMMSA) in 1983.
  • 1995 Alta Pimeria and Kennecott outline a potential target of a million ounces of gold and 50 million ounces of silver.
  • 1997, Bell Coast Capital Corp (BCCC) conducted a helicopter supported, 31-hole, 2,500 m diamond drill program from 6 to 8 drill pads. This first-pass drilling program returned excellent results, but BCCC withdrew from the project due to difficulty in acquiring financing during a period of very low gold and silver prices.
  • BCCC completed an extensive program of geochemical sampling and mapping, resulting in the discovery of three large anomalies.

Historic Articles

Articles in the Engineering and Mining Journal 1897 and 1900 give some details about past developments and production of gold and silver from the Copalquin Mining District. Click the links below to open the articles in a separate window. Close the window to return to the site.

Engineering and Mining Journal 12th May 1900
Engineering and Mining Journal 21st August 1897
Engineering and Mining Journal 4th September 1897