PROJECTS - Don Sixto (La Cabeza)
Geology
The rocks underlying the Don Sixto Prospect are limited to the upper part of the Choiyoi Formation. Only the ignimbrite and its various phases are exposed while the underlying volcaniclastics have been intersected in drill holes. In detail the ignimbrite includes, in decreasing abundance, magmatic phases of felsic porphyry, breccia, monzonite, trachyandesite/basalt, and crystal vitric tuff. These different phases are thought to have accompanied periodic pulses of eruption resulting in inter-lensing relationships within the main rhyolitic unit. In particular, the breccia zones occurring as discontinuous lenses of rhyolitic ejecta appear concordant and in sequence with the enclosing ignimbrite making their occurrence depositional rather than structural. Their attitudes as determined by surface mapping and drill hole intersections reflect the attitude of the entire ignimbrite sequence, at least within the vicinity of the prospect area.
A felsic porphyry which commonly occurs near the base of the ignimbrite and close to the contact with the underlying volcaniclastics appear to be preferentially mineralized in some deposits. In the Mandibula and Labio deposits, the breccia close to the underlying vocaniclastics is the preferred host. The contact zone with the volcaniclastics presents an excellent guide to additional ore.
The general structural trend within the prospect area is north to northwesterly and east-west. The vein systems and recognized faults follow this same general trend. Based on the attitude of the breccia in Mandibula, the rhyolite-ignimbrite sequence in the Don Sixto prospect strikes northwesterly with an average dip of 65 degrees northeast. Other structural features such as chilled contacts and flow banding are indicative of recurring episodes of volcanic extrusion.
Deposit Types
All of the gold deposits in the Don Sixto Prospect are either quartz vein fillings or quartz replacements in shear and/or breccia zones in volcanics. The veins are generally discontinuous and lenticular, pinching and swelling within short distances. The thickness of the individual veins range from a typical 2m to a maximum 15m at the Cuello deposit. The longest vein is found at Madibula where it follows the footwall of a breccia zone for some 800m.
Mineralisation
Mineralisation in the Don Sixto Prospect is essentially a gold-silver, silica-sericite/illite-adularia low sulphidation epithermal system with low pyrite (<2%), minor clay alteration, and minor base metal mineralisation. Variations in style and mineral assemblages between the individual deposits seem to indicate multiple phases of mineralisation within their immediate area. In general, mineralisation appears to be stratigraphically controlled, preferring horizons between the various volcanic phases and the contact with the underlying volcaniclastics.
Map inspection at Labio with Mandibula Ridge in background
Geological Mapping
Geological mapping completed on the Don Sixto prospect during the period 1996 - 1998 includes 1:5000 and 1:2500 scale mapping over the main project and some limited 1:1000 scale mapping over a number of prospect areas.
- 1:1000 Scale: El Cuello, El Ojo, La Mandibula, La Luna, El Cachete and El Cuello.
- 1:2500 Scale: Mapping over the terrain containing the Don Sixto gold prospects.
- 1:5000 Scale: Mapping over the remainder of the Don Sixto grid
This PDF is an English translation of the original paper:
Delendatti, G.L., 2005: Don Sixto: Un Depósito Epitermal Aurífero de Baja Sulfuración en el Bloque de San Rafael, Mendoza, Argentina. VIII Congreso Argentino de Geología Económica, 15, 16 y 17 de Noviembre de 2005, pp. 199 - 206., Ciudad de Buenos Aires.
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