43-101 2008 Technical Report On The La Fortuna Project, Durango ...

5.0 DEPOSIT TYPE
El Castillo is an epithermal gold prospect. Epithermal deposits form in the shallow parts of magmarelated
hydrothermal systems (Figure 5). They are generally associated with volcanism and intrusions of
calc-alkaline magmas, commonly in sub-aerial volcanic arcs. There are two end-member styles of
epithermal mineral deposits: low-sulphidation and high-sulphidation (Figure 5-1). Mineralization at El
Castillo is somewhat enigmatic, partly due to the lack of detailed geologic study, but in general shares
more characteristics with low-sulphidation type of epithermal mineralization than high-sulphidation
mineralization (Cook and Simmons, 2000; White and Hedenquist, 1995).
Figure 5. Diagram of the geologic environment for epithermal deposits.
Sulphide mineralization is generally introduced along faults and fractures although mineralization can also
be disseminated in permeable rock strata. Sulphide assemblages include electrum, native gold, native
silver, argentite, pyrargyrite, proustite, chalcopyrite, sphalerite, galena, tetrahedrite and occasional
telluride minerals. Common gangue minerals include quartz, chalcedony, adularia, calcite and amethyst.
Vertical metal zonation is manifested with higher amounts of gold, silver, or gold and silver along with
mercury, tellurium and antimony in the upper portions of the system, and higher lead, zinc and copper
contents at deeper levels.
Gold and silver grades in low-sulphidation epithermal systems can be very high, occasionally reaching
gold grades on the order of tens-of-grams of gold per tonne and kilograms of silver per tonne. Lowsulphidation
epithermal deposits typically average around 770,000 tonnes and average 7.5 grams per tonne
(“g/t”) Au, 110 g/t Ag with minor Cu, Zn and Pb (Panteleyev, 1996). It should be noted that these grades
and tonnages are representative of vein-type low-sulphidation deposits.
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