Mexico

Dolores Mine

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Overview

Mine TypeOpen Pit
StatusActive
Commodities
  • Silver
  • Gold
Mining Method
  • Truck & Shovel / Loader
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SnapshotThe Dolores mine is an open pit silver-gold mine. In 2016 was commenced underground mining and after nearly 6 years of mining the underground operation was put in care and maintenance in April 2022.

Mining and stacking activities are expected to be completed by Q3 2024, with residual leaching to follow for years thereafter.

Owners

SourceSource
CompanyInterestOwnership
Pan American Silver Corp. 100 % Indirect
Compañía Minera Dolores, S.A. de C.V. (operator) 100 % Direct
Pan American Silver has 100% ownership of the Dolores mine and the mining concessions, through its wholly-owned subsidiary Compañía Minera Dolores S.A. de C.V.

Contractors

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Deposit type

  • Epithermal
  • Vein / narrow vein
  • Breccia pipe / Stockwork

Summary:

Dolores is a low sulphidation epithermal deposit with strong structural control. Northeast-striking faults, perpendicular to the structural grain, locate many mineral deposits in the Sierra Madre Occidental. However, regional controls at Dolores are unclear where mineralized faults are north-northwest striking. There is no transverse structure apparent on geological maps or satellite imagery. The mineralized structures have a typical Sierra Madre, or Laramide, trend, a direction probably inherited from the basement of elongate terranes.

Local structural controls are better understood. Sometime after eruption of the Upper Volcanic Series, there was a northeast-southwest extensional regime, with a component of dextral strike-slip, creating dilation on northwest-striking faults. It also caused local dilational jogs that allowed emplacement of dikes, hydrothermal breccias, and sheeted veins. It is likely that the diorite stock-diatreme complex was the main heat engine that drove the hydrothermal system and provided the source of metals. It may have also been emplaced into a space created by a dilational jog. Geopetal structures and low temperature minerals suggest Dolores developed close to the original surface and has not been strongly eroded.

High silver and gold grades occur over a wide vertical interval at Dolores. This is unusual for most low sulphidation epithermal deposits, which tend to have narrow vertical intervals of high grade.

Lithology was important for localizing high grade. Although the principal control on fluids was semi-regional faults (San Francisco and Alma Maria), some host rocks were ideal for fracturing. Others were ductile and less amenable to mineralization. For example, historic workings in the East Dike targeted a hydrothermal breccia hosted by a latite dike that disappears where the structure passes into country rocks. This, and many other examples, highlights the importance of brittle host rocks. Latite dikes were ideal while the surrounding andesites were a poorer host.

Vein textures, the occurrence of adularia, and the simple sulphide mineralogy confirm Dolores is a low sulphidation epithermal deposit although it lacks the typical complex crustiform banding found in most low sulphidation veins (e.g. Hishikari in Japan and Kupol in Russia). This implies relatively few mineralizing and boiling events in the conduits. Local advanced argillic alteration along the East fault suggests the potential presence of high sulphidation-type mineralization (Staude, 2001).

Major post-mineralization offsets of up to 500 m occurred on the principal faults at Dolores. Mineralization effectively sealed the San Francisco structure. Therefore, the focus of post-mineralization movement jumped west by up to 100 m. This resulted in a major fault zone, dominated by milled and foliated smectitic rock.

Silver and gold mineralization at Dolores is hosted in north-northwest trending hydrothermal breccias and sheeted vein zones in the order of 5 m to 10 m wide. Most high-grade mineralization occurs along three major structures that provided the conduit for metal-bearing fluids. Silver and gold mineralization identified on the surface at Dolores lies over an area 4,000 m long and up to 1,000 m wide, at elevations ranging between 1,100 m to 1,700 m above sea level. Hydrothermal breccias carry the highest silver and gold grades and pass outward into vein stock works. The veins are thin, rarely over 30 millimetres (mm), and tend to occur as sheeted swarms. Economically mineable grades occur where the veins are sufficiently closely spaced.

The highest grade mineralization occurs within the San Francisco Breccia, a well-defined and continuous hydrothermal breccia and stockwork zone that occurs in the immediate footwall of the post-mineralization San Francisco Fault. The breccia trends further away from the fault towards the north until it joins a second major breccia zone known as the Alma Maria Breccia. Other high-grade zones split and re-join, forming diamondshaped structures and steeply pitching mineralization shoots. The San Francisco Fault marks a profound drop in grade and the hangingwall is mostly devoid of silver and gold mineralization.

A sub-vertically pitching mineralization shoot occurs where the San Francisco and Alma Maria Breccias meet, parallel to the intersection. Clearly, this was a site of increased permeability for hydrothermal fluids. High grades also occur in the diorite stock-diatreme complex in the pit. The diorite formed an ideal brittle host for fracture, allowing more extensive brecciation and stock working. It may also have been the main upflow centre for hydrothermal fluids.

Mineralization is generally associated with quartz and may be composed primarily of iron oxides, silver sulphosalts, electrum, and native gold in the oxidized zone and with pyrite, silver sulphides, native silver, visible gold, galena, and sphalerite deeper in the sulphide zone. Local acanthite and visible gold occur in a variety of settings, including hydrothermal crackle breccias and in thin quartz-dominated veins. Hydrothermal breccias carry the highest silver and gold grades and vary from crackle to very milled types. Crackle types were more permeable, and they commonly show coarse quartz + sulphide (pyrite, sphalerite, and galena) + fluorite gangue. They pass outward into vein stock works. Hydrothermal breccias commonly include veins of quartz, quartzcalcite, fluorite, and anhydrite and mostly developed after the sheeted vein swarms. Some diffuse areas of sugary, silicified rock with coarse adularia and high silver and gold grades also occur.

Most veins at Dolores are relatively simple, with only weak crustiform texture. They comprise euhedral comb quartz and commonly show aggregates of very fine-grained drusy quartz. They are thin, rarely over 30 mm, and tend to occur as sheeted swarms. Economically mineable grades occur where the veins are sufficiently closely spaced.

Vein fill progresses from high temperature (>200°C) minerals, such as epidote, to low temperature (150°C to 200°C) minerals such as colloform chalcedony, adularia, amethyst, laumontite, and other zeolites. Geopetal structures occur in some veins and indicate high levels in the epithermal system. The proximity of high and low temperature minerals suggests rapid cooling of fluids, perhaps due to uplift or a rapidly waning hydrothermal system. The presence of zeolites indicates very alkaline fluids.

Base metal sulphides appear to increase at depth, with widespread coarsely crystalline sphalerite, galena, and minor chalcopyrite. Base metal sulphides are particularly abundant in the deeper parts of the stock-diatreme complex in the pit. The most dominant sulphide mineral accompanying the mineralization is pyrite, in concentrations of between 1% and 2%, with intense pyritization of approximately 6% at the lithological contacts.

Reserves

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Mining Methods

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Comminution

Crushers and Mills

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Processing

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Production

CommodityUnits2024202320222021202020192018201720162015
Silver koz  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe5,1224,0814,2323,8384,250
Gold koz  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe11813710310379
All production numbers are expressed as metal in doré. ^ Guidance / Forecast.

Operational metrics

Metrics202320222021202020192018201720162015
Ore tonnes mined  ....  Subscribe  ....  Subscribe  ....  Subscribe
Waste  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe
Tonnes milled  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe6,777 kt6,903 kt6,605 kt6,307 kt6,109 kt
Daily milling rate  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe
Daily milling capacity  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe20,000 t20,000 t20,000 t16,200 t
Annual production capacity  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe7,500 koz of silver metal in doré
Annual production capacity  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe200 koz of gold metal in doré

Production Costs

CommodityUnits20242023202220212020201920182017
Total cash costs (sold) Gold USD  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe
Total cash costs (sold) Silver USD  ....  Subscribe 3.09 / oz **   -1.87 / oz **   -1.65 / oz **  
All-in sustaining costs (sold) Gold USD  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe
All-in sustaining costs (sold) Silver USD  ....  Subscribe 15.5 / oz **   16.4 / oz **   10 / oz **  
^ Guidance / Forecast.
** Net of By-Product.

Financials

Units20242023202220212020201920182017
Capital expenditures (planned) M USD  ....  Subscribe
Sustaining costs M USD  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe 49.7   48.5   38.4  
Capital expenditures M USD  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe 47.7   59.5   85.4  
Revenue M USD  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe 248.7   236.8   197.7  
Operating Income M USD  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe -47.3   -34.7  
Pre-tax Income M USD -35.6   -0.5  
After-tax Income M USD -10.8   11.2  

Heavy Mobile Equipment

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Personnel

Mine Management

Job TitleNameProfileRef. Date
....................... Subscription required ....................... Subscription required Subscription required Apr 10, 2024
....................... Subscription required ....................... Subscription required Subscription required Apr 10, 2024

EmployeesContractorsTotal WorkforceYear
...... Subscription required 2021
...... Subscription required ...... Subscription required 2014

Aerial view:

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