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In the past 15 years several expeditions by French, American and especially Italian cavers have surveyed over 15 km of salt cave passages in the Cordillera de la Sal, close to San Pedro de Atacama village (Atacama Desert, Northern Chile). Over 50 caves have been explored up to now at an elevation around 2,500 m asl. These karst systems are characterized by in-cave temperature of around 17 °C and a relative humidity always very low, with a maximum of 15%. This extreme aridity is due to the severe conditions of the area with only a couple millimeters annual rainfall and several years without rain. Currently the rare precipitation events are enough to allow the dissolution of the salt rock and crusts, and the deepening of underground meandering river passages. Moreover, after the sporadic rain events, the water penetrating the cave’s host rock along fractures and bedding plains leads to the dissolution of primary minerals and allows the formation of seeping brines with dissolved salts. Both these processes selectively add solutes to the incoming undersaturated rainwater. The evaporation of these resulting salt-rich fluids at the cave atmosphere interface causes secondary minerals to precipitate. Mineral samples have been collected in eight caves, and include stalactites, flowstones, precipitates that form crusts in the streambeds and at the groundwater seeps, parietal coatings, earthy masses from the cave floors and efflorescence salts on ceiling rock outcrops. Most secondary deposits are composed of halite, but also other halides, carbonates, sulphates, nitrates, phosphates, and silicates have been discovered. Among the sixteen observed minerals, antarcticite, leonite, darapskite, blödite, atacamite and anhydrite are worth mentioning. The peculiar climate (extremely arid) and the very special environment dominated by NaCl and CaSO4, allow the crystallization primarily of halite. Atacamite was found where local enrichment in Cu (of hydrothermal origin) occurs, and antarcticite precipitates by the final evaporation of SO4-depleted brine (after early precipitation of anhydrite). Among sulphates, the metals necessary for the formation of these mineral species (magnesium, potassium, sulphate) derive from the cave sediments while nitrates are supplied by bird guano. Salt mineral precipitation is controlled by the temperature dependence solubility of the species in saline water, so that different secondary minerals were observed.

First results of a study on hypogenic caves in Sicily are presented. Inactive water-table sulphuric acid caves and 3D maze caves linked to rising of thermal waters rich in H2S were recognized. Cave patterns are guided by structural planes, medium and small scale morphological features are due mainly to condensation-corrosion processes. Calcite and gypsum represent the most common cave minerals. Different types of phosphates linked to the presence of large bat guano deposits were analyzed.

In March 2009 the Guacamaya Cave was discovered on the Auyan Tepui. It represents one of the longest caves explored on this table mountain, the only one known today with a complete horizontal development, comparable with those of the Brewer Cave System, in the Chimanta Tepui (the world largest sandstone cave). Guacamaya Cave presents peculiar morphologies, developed along an obvious bed of iron hydroxides and amorphous silica (Banded Iron Formation, BIF) interposed between hard and massive quartzite banks. In the walls around this layer, a variety of opal speleothems, of unusual dimensions and shapes, together with gypsum flowers and crusts have been documented. Here we present a compositional and morphological characterization for the BIF layer and one tufa-like bio-speleothem. The speleogenetic control exerted by the BIF stratum is discussed, and in relation to collapse morphologies observed on the surface. An attempt to date the bio-speleothem with the U-Th system shows the difficulties of applying this method to these silica formations, because of post-depositional alteration in this porous material.

La Cueva Guacamaya, esplorata nel marzo 2009 dall’elicotterista Raul Arias, è la più vasta cavità a sviluppo orizzontale conosciuta nel massiccio quarzitico dell’Auyan Tepui, nella Gran Sabana Venezuelana. A differenza delle altre cavità esplorate nell’area in precedenti esplorazioni dell’Associazione La Venta, questa grotta presenta morfologie peculiari, sviluppandosi lungo un sottile interstrato di ossidi e argille che interrompe la serie quarzitica della Formazione Mataui. La presenza di speleotemi di opale, di svariate forme e dimensioni notevoli, unite alla presenza di infiorescenze di gesso, per la prima volta segnalate in ambiente quarzitico in tale abbondanza, fanno di questa cavità un’interessante oggetto di studio sia per gli aspetti mineralogici, sia per un futuro progetto di datazione e geochimica degli speleotemi di opale. In March 2009 the Guacamaya cave was discovered on the Auyan Tepui by the helicopter pilot Raul Arias. It represents one of the longest caves explored on this table mountain, the only one known today with a complete horizontal development, comparable with those of the Brewer Cave System, in the Chimantha Tepui (the world largest sandstone cave). This cave presents typical morphologies, developed along an evident interbed of oxides, amorphous silica and clay interposed between hard quartzitic massive banks. In the walls around this layer, a variety of opal speleothems, of unusual dimensions and shapes, together with gypsum flowers and crusts have been documented. This preliminary study focuses on the general morphology of the cave conduits and on the mineralogical compositions and features of the opal-gypsum speleothems.

Se l’esplorazione della Grotta del Re Tiberio, la più importante cavità carsica della Vena del Gesso Romagnola, può dirsi praticamente conclusa, praticamente nulla è stato ancora fatto per definirne l’evoluzione nel tempo di alcune sue forme e sedimenti peculiari. L’analisi di dettaglio delle forme erosivo-dissolutive e dei sedimenti chimici e fisici presenti in due piccole gallerie relitte all’interno della Cava di Monte Tondo e facenti parte del sistema carsico del Re Tiberio, ha permesso di ricostruire la loro storia evolutiva, che ha comportato anche lo sviluppo di alcuni rari speleotemi, tra cui i poolfinger di calcite, i cristalli di gesso epitassiali e gli orli di ossidi di ferro e di gesso secondario che bordano i cristalli della matrice gessosa esposti nelle pareti della grotta, nonché la presenza di cristallizzazioni effimere di epsomite.

La Grotta di Montecchio (254 T/GR, presso Saturnia, provincia di Grosseto) si apre a quota 320 m, in corrispondenza di un limitato affioramento di Calcare Massiccio, prospiciente la valle del Fiume Albegna. Benché nota da tempo, finora non sono stati fatti studi dettagliati di tipo speleogenetico su questa particolarissima cavità. Questa grotta, che si sviluppa per oltre 1700 m, è infatti caratterizzata dalla presenza di una falda di acqua con T poco sopra i 30°C e con un elevato contenuto in solfato, alla profondità di circa 100 metri dall’ingresso: si tratta quindi di una grotta ipogenica attiva. Di particolare interesse è l’abbondanza di gesso, a partire da circa 40 metri di profondità, prodotto dalla reazione tra acido solforico e roccia carbonatica. Tale processo, che è avvenuto in condizioni aeree (ossigenate), ha creato anche una serie di morfologie particolari come le piccole tasche di sostituzione e le bubble trails. La parte inferiore della cavità presenta depositi di calcite flottante di spessore anche superiore a 1 metro che testimoniano lo stazionamento di acque, probabilmente termali, in ambienti con notevole evaporazione legata a correnti d’aria. Undici campioni di prodotti di alterazione della roccia sono stati sottoposti ad analisi diffrattometrica ed esaminati al microscopio elettronico dotato di microsonda per analisi chimiche semiquantitative. Tali analisi hanno evidenziato la presenza di materiali residuali (quarzo, feldspato), alcuni ossidati (ematite, goethite e boehmite), ma soprattutto materiali di alterazione come clorite ed illite. Di particolare interesse sono i prodotti di alterazione acida sia della roccia carbonatica (gesso) sia delle argille (alunite, jarosite e caolinite). Questi minerali sono strettamente legati alle fasi speleogenetiche della grotta, essendo formati dall’interazione della roccia madre con i vapori sulfurei provenienti dalla falda termale. The Montecchio cave (254 T/GR, close to Saturnia, Grosseto province) opens at 320 m asl, in a small outcrop of Calcare Massiccio, close to the Albegna river. Although known since a long time, there are no speleogenetical studies on this very special cave. This cave, with a development of over 1700 m, is characterised by the presence of the thermal aquifer at a depth of 100 m below the entrance. The water has a temperature of over 30°C and high sulphate content. The cave can thus be considered an active hypogenic system. The cave hosts large gypsum deposits, starting from 40 m below the entrance. This gypsum derives from the reaction between sulphuric acid and the carbonate hostrock. This process, that occurs in the vadose (oxygen rich) environment, has created a set of typical morphologies such as replacement pockets and bubble trails. The lower part of the cave hosts calcite cave raft deposits over 1 m thick, evidence of standing, probably thermal, water pools in strongly evaporative areas related to strong air currents. Eleven samples of weathering products have been sampled and analysed at the X-ray diffractometer and investigated under SEM/EDAX. These mineralogical analyses have identified residual minerals (quartz, feldspar), some oxides and hydroxides (hematite, goethite and boehmite), but especially weathering products such as chlorite and illite. The products of acid weathering are particularly interesting, like those derived from calcite (gypsum) and from clays (alunite, jarosite and caolinite). These minerals are strictly related to the speleogenesis of the cave, having formed by the interaction between the host rock and the sulphuric vapors rising from the thermal aquifer.

A series of mineral crusts and speleothems currently forming in the abandoned tunnels and shafts of the Pb- Zn-As-Sb Argentiera mine (Sassari) have been sampled and analysed. Over 20 crystalline phases have been determined, among which many sulphates (barite, copiapite, epsomite, gypsum, jarosite, melanterite, metavoltine, and sideronatrite) and carbonates (aragonite, calcite, dypingite, giorgiosite, hydromagnesite, and hydrozincite). Also several oxides (hematite, akaganeite, and pseudoboleite), hydroxides (goethite, lepidocrocite, and todorokite) and silicates (quartz, illite, and feldspar) have been found. The most interesting mineral paragenesis (akaganeite, dypingite, giorgiosite, and hydromagnesite) has been discovered on a nail that has given both iron and magnesium necessary to their formation.

Sa Corona ‘e sa Craba (Barbusi, Carbonia, Southwest Sardinia) is a natural cave almost entirely developed within a quartzite vein. Its natural entrance, enlarged during mining operations, opens at 260 m asl. The cave is composed of an over 200 m long and 20 m wide gallery developed in a NW-SE direction. 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 pathways. These samples ranged in color from yellow to red, purple, brownish, grey, white, pinkish, bluish and black. Beside 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.

La Tagusan Cave è una cavità di attraversamento che si apre nel massiccio calcareo che ospita la famosa grotta Porto Pricesa Undergroud River nell’isola di Palawan (Filippine). Al suo interno sono state rivenute alcune pisoliti di colore nero che sono state campionate e quindi analizzate dal punto di vista tessiturale e mineralogico. Le analisi al microscopio ottico hanno evidenziato come queste pisoliti non siano omogenee ma siano costituite da un nucleo spesso costituito da una aggregazione di ooliti giallastre su cui si è depositata un’alternanza di sottili strati picei e rossastri. L’analisi mineralogica delle bande di accrescimento ha evidenziato la presenza, oltre a fosfati di calcio praticamente amorfi, di robertsite [Ca2Mn3(PO4)3O2•3H2O], un fosfato che non era mai stato segnalato prima in grotta. Sempre in queste bande, sulla base degli esami röntgenografici e delle analisi EDAX, si è ipotizzata la presenza anche di janggunite [Mn5-x(Mn,Fe)1-xO8(OH)6], di cui però non si è raggiunta la certezza. Nel nucleo invece è stato possibile identificare la presenza di strengite-Al [(Fe,Al) (PO4) •2H2O]. La genesi di queste particolari pisoliti è da mettere in relazione con i processi di digestione biologica del guano che all’inizio della loro evoluzione doveva essere abbondante nelle acque che fluivano nella grotta, mentre ora, l’apporto idrico è molto più scarso e proviene da stillicidi che hanno scarsa relazione con il guano medesimo. The Tagusan cave is a hydrologic tunnel in the karst massif hosting the famous Porto Pricesa Underground River in the Palawan Island (Philippines). It hosts some speleothems among which are worth to be cited some black pearls. A few of them have been sampled to be analyzed from the textural and mineralogical point of view. The optical microscope analyses put in evidence that the inner structure of these pearls is un-homogeneous, consisting of a nucleus often made by aggregates of yellowish oolites covered by alternated pitch-dark and reddish layers. The mineralogical analyses find out that the growing layers consist of amorphous phosphates and robertsite [Ca6Mn9(PO4)9O6(H2O)6•3(H2O)], which is here recognized, for the first time, as cave mineral. The x-ray patterns and the EDAX analyses suggest also the presence of janggunite [Mn5-x(Mn,Fe)1-xO8(OH)6], but no definitive proof of it has been yet achieved. Strengite-Al, [(Fe,Al)PO4•2H2O)] is the main component of the yellowish oolites in the pearl’s nucleus. The genesis of these peculiar cave pearls is strictly related to the biological digestion processes of the guano deposits. In fact at the beginning of their evolution the feeding water directly crossed guano deposits, while now the few still active dripping practically has no contact with it.