Sa Corona ‘e sa Craba (Barbusi, Carbonia, Southwest Sardinia) is a natural cave entirely developed within a quartzite vein. Its natural entrance, enlarged during mining operations, opens at 260 m asl. It is composed of an over 200 m long and 20 m wide gallery developed in a NW-SE direction. The cave was discovered in 1971 by cavers of the Gruppo Ricerche Speleologiche E.A. Martel of Carbonia and, because of its mineralogical interest, became immediately the prey of rock hounds and mineral vendors. Unfortunately, this “plundering” enormously compromised the natural beauty of this cave, partly destroying a true scientific treasure. The entire cave is characterized by large passages and clear signs of dissolution by acid solutions in subaerial conditions. These might have derived from the oxidation of sulfide ore bodies present in the neighbourhood or by rising of hydrothermal fluids. The Corona ‘e sa Craba area, in fact, was explored for Pb, Zn and Ba ores in the early 1930s, and economic exploitation went on for a little more than 30 years after 1950. Despite over 20 years of high interest for mineral collectors in this cave, only five minerals were known from this locality: barite (in gorgeous crystals turning bluish when exposed to light), calcite, quartz, dolomite, and aragonite. During our surveys we collected over 50 small samples of crusts, coatings and spars from all over the cave, on which we performed X-ray diffraction analysis in order to understand the speleogenetic pathway. These samples ranged in color from yellow to red, purple, brownish, grey, white, pinkish, bluish and black. Besides the already known minerals, the following have been discovered for the first time within this cavity: sulfide: cinnabar; sulfates: alunite, natroalunite, basaluminite, walthierite and gypsum; phosphates: taranakite, spheniscidite, robertsite, Al-rich strengite, hydroxylapatite, vashegyite and an unnamed Pb-Mo oxide phosphate; silicates: halloysite, lizardite and clay minerals of the illite and smectite group; oxyhydroxides: hematite, goethite, pyrolusite and todorokite. The presence of a large colony of bats, the unusual quartzite bedrock in which the cave is developed, and the combined presence of sulfides and carbonate-rich drip water, have made of this cave a unique mineralogical environment of great scientific interest.
Baldoni Eleonora, De Waele Jo, Galli Ermanno, Messina Mauro, Onac Bogdan P., Sanna Laura, et al. (2013). Mineralogy and Speleogenesis of the Corona ‘e sa Craba quartzite cave (Carbonia, Southwestern Sardinia). Bologna : Istituto Italiano di Speleologia.
Mineralogy and Speleogenesis of the Corona ‘e sa Craba quartzite cave (Carbonia, Southwestern Sardinia)
DE WAELE, JO HILAIRE AGNES;SAURO, FRANCESCO;
2013
Abstract
Sa Corona ‘e sa Craba (Barbusi, Carbonia, Southwest Sardinia) is a natural cave entirely developed within a quartzite vein. Its natural entrance, enlarged during mining operations, opens at 260 m asl. It is composed of an over 200 m long and 20 m wide gallery developed in a NW-SE direction. The cave was discovered in 1971 by cavers of the Gruppo Ricerche Speleologiche E.A. Martel of Carbonia and, because of its mineralogical interest, became immediately the prey of rock hounds and mineral vendors. Unfortunately, this “plundering” enormously compromised the natural beauty of this cave, partly destroying a true scientific treasure. The entire cave is characterized by large passages and clear signs of dissolution by acid solutions in subaerial conditions. These might have derived from the oxidation of sulfide ore bodies present in the neighbourhood or by rising of hydrothermal fluids. The Corona ‘e sa Craba area, in fact, was explored for Pb, Zn and Ba ores in the early 1930s, and economic exploitation went on for a little more than 30 years after 1950. Despite over 20 years of high interest for mineral collectors in this cave, only five minerals were known from this locality: barite (in gorgeous crystals turning bluish when exposed to light), calcite, quartz, dolomite, and aragonite. During our surveys we collected over 50 small samples of crusts, coatings and spars from all over the cave, on which we performed X-ray diffraction analysis in order to understand the speleogenetic pathway. These samples ranged in color from yellow to red, purple, brownish, grey, white, pinkish, bluish and black. Besides the already known minerals, the following have been discovered for the first time within this cavity: sulfide: cinnabar; sulfates: alunite, natroalunite, basaluminite, walthierite and gypsum; phosphates: taranakite, spheniscidite, robertsite, Al-rich strengite, hydroxylapatite, vashegyite and an unnamed Pb-Mo oxide phosphate; silicates: halloysite, lizardite and clay minerals of the illite and smectite group; oxyhydroxides: hematite, goethite, pyrolusite and todorokite. The presence of a large colony of bats, the unusual quartzite bedrock in which the cave is developed, and the combined presence of sulfides and carbonate-rich drip water, have made of this cave a unique mineralogical environment of great scientific interest.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
