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.

Litholo ........

Mining at Dolores has been ongoing since 2008 using conventional open pit methods with excavators, shovels, loaders, and haul trucks. Ore grade control drilling is carried out using angled RC drilling to provide closer spaced sample data for a grade control estimate, which is used to mark out the ore and waste mining boundaries. The grade control holes are oriented perpendicular to the strike of the deposit on sections spaced every 15 m along strike and every 10 m to 15 m across strike. Drillholes are approximately 43 m long, which results in a nominal vertical span of 30 m, equal to four bench heights. The drillhole pattern is offset with 25% of the holes drilled from each bench to provide full coverage. The RC drillholes are logged for lithology and oxidation and sampled every 2 m.

Ore and waste material is drilled and blasted using 135 mm diameter holes, using a nominal pattern of 8.5 m deep blast holes spaced 4.5 m along strike and 4.5 m across strike. Explosives used are ANFO. Ore and waste are usually blasted separately, and a blast movement monitoring system is used to manage ore loss, dilution, and material misclassification.

Golder recommended bench heights of 7.5 m with 7.5 m wide catch benches located after each bench for mining areas within 30 m of the surface, and catch benches located each third bench or each 22.5 m vertically for mining areas below 30 m. For pre-split and trim mining, the recommended catch bench width is 9.1 m, with a benc ........

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