The Copalquin District Mining Concessions, Mexico

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

Location: 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 executing 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 is a maiden JORC resource estimate for the El Refugio area late Q4 2021 while continuing to drill and expand the deposit strike length.

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.

Over 55 diamond core drill holes have been completed along the El Cometa-El Refugio structure with every hole returning reportable gold-silver intercepts. El Refugio is developing as a high-grade deposit of gold and silver and work is progressing to produce a maiden JORC resource estimate towards the end of Q4 2021.

Figure 1 – Copalquin District mining concession area with the drilling highlights from the first 12 months of drilling.

At 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.

Figure 2 – Long section from main El Refugio structure to Los Reyes.

1Gold Eq. = gold equivalent. Silver Eq. = silver equivalent. Calculated using 70 g/t Ag = 1 g/t Au, based on gold price of USD1,610/oz and silver price of USD23/oz

Figure 3 – Long section for El Refugio showing the drill hole pierce points. This is the main area for the Maiden JORC resource estimate to be completed late Q4 2021.

1Gold Eq. = gold equivalent. Silver Eq. = silver equivalent. Calculated using 70 g/t Ag = 1 g/t Au, based on gold price of USD1,610/oz and silver price of USD23/oz

Maiden Resource Estimate Progress

The current drilling through to CDH-090 consists of holes in the western extents of the current El Refugio maiden resource estimate (MRE) area will complete the database for the initial resource modelling to be undertaken by AMC Consultants. The drilling and the assay results are expected to be available late October 2021 with the resource estimation work being completed late November 2021. The independent site visit will be conducted in September 2021.

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

1Gold Eq. = gold equivalent. Silver Eq. = silver equivalent. Calculated using 70 g/t Ag = 1 g/t Au, based on gold price of USD1,610/oz and silver price of USD23/oz


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.
  • UC Resources explored at Copalquin from 2003 – 2007, drilling 39 diamond core holes for 4,200m. UC also completed geochemical sampling and an ASTER study. UC experienced funding difficulties and ceased activities late 2007.

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