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Dolores Mine
The Dolores open pit silver-gold mine is located in the Sierra Madre Occidental mountain range in the state of Chihuahua, in the municipality of Madera, approximately 250 kilometres west of the city of Chihuahua. The area of the concessions is 27,700 hectares.
The Dolores mine is located in the Sierra Madre Occidental mountain range, which comprises a long northwest trending volcanic plateau. The region is dominated by rhyolitic ash flow tuffs of Oligocene age known as the Upper Volcanic Series. The Upper Volcanic Series unconformably overlies rocks of the slightly older Lower Volcanic Series which are comprised primarily of andesites with interlayered felsic ash flow tuff deposits of Eocene age. The deposition of the Lower Volcanic Series was accompanied by the emplacement of quartz diorite and granodiorite batholiths and small intrusive bodies. The majority of the epithermal and porphyry related precious metals deposits in the Sierra Madre are hosted in the Lower Volcanic Series. The oldest structural episode is related to the Laramide orogeny, which produced east striking, steeply dipping strike slip faults. Later extensional forces resulted in the regional development of north-south to northwest-southeast striking sub-vertical normal faults. The structures hosting mineralization in the Dolores area are believed to have controlled emplacement of a series of north-northwest trending andesite to latite intrusions. Zones of permeability associated with these faults and intrusive contacts formed conduits for the ascending mineralizing hydrothermal fluids.
The Dolores project is underlain by the Lower and Upper Volcanic Series. At the mine site the Lower Volcanic Series consists of gently tilted lavas, flow breccias, and tuffaceous rocks with a minimum thickness of 700 metres. It is conformably overlain by 100 to 200 metres of felsic latite volcaniclastic breccia. These units are overlain by the Upper Volcanic Series, which comprise a volcaniclastic assemblage of mostly felsic ignimbrites and tuffs. The Upper and Lower Volcanic Series are separated by a distinctive erosional rubble zone unconformity that formed after development of north-northwest trending anticlinal uplift. Subsequent erosion has exposed mineralized rocks of the Lower Volcanic Series in the Dolores district.
Gold and silver mineralization at Dolores is present as low to medium sulphidation, epithermal gold-silver bearing veins, silica stock works, breccias, and replacements. The system is mostly structurally controlled within a north-northwest striking extensional fault system. Gold and silver mineralization identified on the surface at Dolores lies over an area 4,000 metres long and up to 1,000 metres wide, at elevations ranging between 1,100 metres to 1,700 metres above sea level. The extent of mineralization at depth and along strike has not been fully defined.
Relatively deep mineralization tends to be located in high grade veins typically of five to ten metres wide, while at higher elevations these feeder veins grade into wider, lower grade stock works, veinlets, and disseminations toward the less competent and more permeable overlying latite flows and tuffs of the Lower Volcanic Series. These wider areas are on the order of a few hundred metres. Near the surface, mineralization shows a strong structural control, but widens out owing to development of breccia and fractures adjacent to the main mineralizing conduits. The main mineralization occurs as a series of parallel structures trending to the north-northwest and dipping steeply to the west.
Mineralization is generally associated with quartz and may be composed primarily of iron-oxides, silver sulfosalts, 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.
625 Howe Street, Suite 1440
Vancouver, British Columbia
V6C 2T6 Canada
Tel: (604) 684-1175
Fax: (604) 684-0147
E-mail: info@panamericansilver.com