Cerro Granadas, Rinconada Department, Jujuy Province, Argentinai

Regional Level Types
Cerro Granadas	Volcano
Rinconada Department	Department
Jujuy Province	Province
Argentina	Country

Volcano.
Elevation: 4,184 m. asl.

The presence of sapphires in alluvial deposits has been identified in the vicinity of the Granadas Hill, West of the Sierra de la Rinconada, in the Northwest corner of the Republic of Argentina. The place is accessed by a road that connects Abra Pampa with Mina Pirquitas. Detailed exploration of the deposits has not been performed even though the sampling sites have shown that the found concentration exceeding 10 grams per cubic meter. Taking into account the extension of the volcanic activity responsible for the transport of sapphires to the surface, it is estimated that it has all the conditions favourable to the discovery of economically viable deposits of gem-quality sapphires in the Puna Jujeña. Coordinates are 22° 30´ S latitude and 66 ° 30´W longitude.

History of the discovery:
The discovery of sapphires in alluvial sediments of the Puna Jujeña was carried out in 1991 on the occasion of the exploration of alluvial gold. The first determinations by x-ray diffractometry were performed by X.O. Morello (CNEA: National Atomic Energy Commission) and its existence was reported by Zappettini and Segal (1994). Other subsequent findings were communicated by Sheridan and Gay (1995). The studies carried out on the material collected were synthesized by Zappettini et al.(1997).

Regional Geology:
The geology of the region is composed of a sedimentary Ordovician basement that hosts gold vein mineralization and on which rests a sequence of Tertiary volcanosediments, in turn covered by a group of andesitic-dacitic lava with interbedded ignimbritics, dacitic and rhyolitic domes are associated with it. The erosion of the previous units resulted in the formation of significant alluvial deposits.

Morphology of deposits:
Recognized manifestations are of the alluvial type. Sapphire crystals occur in sediments consisting of quartz, lithoclasts of sediments and volcanic rocks. As accessory minerals there are, together with corundum, garnet, gold, hercynite, magnetite, hematitized pyrite, monazite and zircon. By its density, the sapphires are concentrated in heavy mineral-rich levels and often accompany the gold "llampo" (finely broken ore).

Mineralogy:
Crystals of corundum and sapphires occur in sediments with little rounding and size between 0.5 mm and up to 1 cm. Observed colours vary from colourless to blue. Crystals are frequent with zoning according to the c-axis, with alternating bands of different colours, just as there are sections in which the distribution of colours is irregular. There are less common varieties of pink. From a crystallographic point of view, the most frequent forms are the rhombohedral, dominant in smaller crystals. Other types correspond to the prism of the first order associated with the pinacoid, with the typical form of Coop. In the crystals, the more elongated prism of the first order is associated with the pyramid. Forms of growth formed by the association of basal faces and the rhombohedron are common. The study of the surface of the crystals identified textures of high-temperature corrosion and the formation of edges of reaction consisting of magnesiferous hercynite. There are also textures produced by mechanical abrasion.
Carbonated and aqueous fluid inclusions and needle-like rutile, magnetite-rich inclusions in the crystals, as well as pyrochlore, albite, likely columbite and mica epigenetics. Determined by scanning electron microscopy and EDAX. Individuals with varying degrees of transport. Also in the form of rosettes.

Other Regions, Features and Areas containing this locality

References