| |  Argentina is definitely not the first country that comes to the mind of most researchers or collectors when thinking about pegmatites. However, this country hosts one of the largest pegmatite provinces of South America, the Pampean Pegmatite Province (PPP), second only to the well-known Eastern Pegmatite Province in Brazil.
 The PPP, as defined by Galliski (1994 a, b), extends from Northwestern Argentina to the middle of the country, roughly from 24º30´ S to 33º30´ S. It comprises 21 orogenic and post-orogenic districts ranging from Upper Precambrian to Lower Carboniferous, some of which have received much more attention than others. The heterogeneity unavoidable when dealing when a number of districts makes it difficult to give general characteristics that apply to all of them. The interested reader is directed to the authoritative work by Galliski (1994 a, b). Most of the pegmatites bear an LCT-type geochemical signature (following the classification of Cerny 1991) and belong to the muscovite and rare-element classes with only the Papachacra district showing a clear NYF-type affinity. The most common pegmatite types are beryl (beryl-columbite and beryl-columbite-phosphate subtypes), complex (spodumene subtype) and albite-spodumene type (Galliski 1994 a). Albite-type are rare, as are lepidolite- and petalite-subtypes. The rare-element pegmatite fields form a belt that runs parallel eastward of the main muscovite class fields.
As it is usually the case, the degree to which these districts have been studied and the amount of minerals mined from the pegmatites are mainly a function of ease of access and proximity to processing centers, one notable exception being the El Quemado pegmatite field.
In general, pegmatites from the PPP have been mined for feldspar, muscovite, quartz and beryl. Some other minerals include spodumene, Bi minerals and U-Nb-Ta oxides, but these are more restricted. Mining has been done mostly by hand, with little mechanical equipment.
Beryl is very common in a number of districts, and was a sought commodity when it commanded high prices; many very small pegmatites, uneconomical for current standards, were mined for beryl. Had not been for this fortunate situation, those pegmatites would remain intact and inaccessible to mineralogical studies. However, not all beryl-bearing bodies are small. The Las Tapias pegmatite hosted one of the largest concentrations of beryl in the world (>3,200 tons have been extracted). This mineral occurred as subhedral crystals in the intermediate zone, in the typical range of colors (greenish, bluish, pale yellow and very rarely pink) but unfortunately all the beryl is cloudy. This pegmatite also produced 300 tons of spodumene, which occurred as prismatic crystals to over 3 m long, and around 8 tons of bismuth minerals. Las Tapias is one of the few pegmatites that have been mined using underground methods.
Gem-quality minerals are very scarce and were recovered as a by-product during the mining for some other minerals. Again, the most outstanding species is beryl, which was found sparingly as attractive greenish, bluish and light to deep yellow crystals. Probably the most productive mines were a few in the Velazco Ranges, around the town of Huaco, in La Rioja Province. Colored tourmaline is very scarce and not gemmy, though some interesting multicolored specimens have been found at the San Elías mine, San Luis Province. Topaz has been found in beautiful crystals only at Papachacra (Catamarca Province), but they are probably more valuable as collector pieces than as gem stock. This locality also produces very nice smoky quartz crystals.
The most serious limitation for the economical exploitation of them is probably not the quality but the reserves. However, this may be desirable when the minerals are sold in the collector market. How many thousand Brazilian quartz crystals can you find for every single Argentine quartz?continued, page 2. | |
|
