|Other regions containing this locality:||The Alps, Europe|
|Name(s) in local language(s):||Cuasso al Monte, Valceresio (Val Ceresio), Provincia di Varese, Lombardia, Italia|
Cuasso al Monte is a municipality in the Province of Varese, whose territory lies at the foot of Monte Piambello, a 1125 m high mountain that dominates the landscape in the area between Lake Ghirla (Valganna) and Lake Lugano.
At Cuasso al Monte a granophyric granite, commercially known as “Red porphyry" ("Porfido rosso"), is quarried. This granophyre contains NYF-pegmatites, famous for rare micromount minerals (REE mineral species and others).
Red-coloured granophyre was quarried and locally used as a building material as early as 1880. Later, granophyre was more extensively quarried for the production of paving stones, worked by artisans which used hand tools like chisels and hammers. At the beginning of the 20th century, the main quarries were located at Cuasso al Monte in front of Via Roma (Cava Grande, Cava Maccalé, and Cava della Motta) and, to the S of Cavagnano, in Val Cavallizza. Around 1910 an aerial railway connecting Cava Grande to Porto Ceresio was built. During World War I, various quarries were opened in proximity of military roads, trenches and fortifications of the Cadorna Line, among which is worth remembering Cava Castello (presently Cava Bonomi) and the so-called “Cava del Prete”. In 1924 the company Puricelli, specialised in quarrying and public works, took over most of the small quarries and developed also the production of crushed stone. In the same period, Sioli (another Milanese public works company) developed the quarry later known as Cava Bianchi (presently Cava Gebel). During the 1950s, the aerial railway was dismantled and substituted by roads for the carriage of quarried material. Since the 1960s, despite the increased demand for quarry material, the increased mechanisation and the shortage of labour caused a progressive reduction in the number of quarries. For several decades only two quarries remain in active operation: Cava Bonomi and Cava Bianchi (nowadays known as Cava Gebel).
At Cuasso al Monte, a Permian caldera structure was identified by Bakos et al. (1990). In this caldera, a thick sequence of volcanic rocks was intruded by a leucogranitic pluton (275 ± 8 Ma) mainly composed of aplitic microgranite and miarolitic granite having a granophyric texture. Aplitic-pegmatitic pods and veins, locally related to large miarolitic cavities, are widespread. Circulation of abundant late hydrothermal fluids was responsible for the crystallisation of many different minerals in the cavities, local alteration of feldspars, and chloritisation of biotite in granite.
The paragenetic sequence at decreasing temperatures from pneumatolytic to HT-MT and LT hydrothermal conditions, observed in the cavities of the Cuasso al Monte granophyric granite, mainly includes: quartz, feldspars, siderophyllite, "zinnwaldite" and muscovite, zircon, Y-REE silicates [allanites and kainosite(Y)], gadolinite group, Y-REE phosphates [monazite-(Ce) and xenotime-(Y)], topaz, sulfides [arsenopyrite, chalcopyrite, galena, marcasite, molybdenite, pyrite, sphalerite, and stibnite], fluorite, aeschynite group, tourmaline, Fe, Ti, Cu oxides [anatase, brookite, cuprite, and hematite], löllingite, apatite group, scandium silicates [bazzite and thortveitite], beryllium silicates [bertrandite and phenakite], titanite, Y-REE carbonates [bastnäsite and synchysite groups], clinochlore and epidote, carbonates and sulfates [ankerite, calcite, cerussite, dolomite, malachite, siderite, and baryte], silver, arsenates and molybdates [adamite, agardite-(Y), pharmacosiderite, powellite, and wulfenite], opal, hemimorphite and pyrophyllite, todorokite and other Mn oxides.
Miarolitic cavities (typically smaller than 1 cm) are abundant throughout the entire outcrop of the granophyric granite. Larger cavities (up to 1 or 2 m) have a characteristic vertically elongated shape and are commonly rooted in an aplitic-pegmatitic pod or vein. Microtextural and structural observations indicate that most of these larger cavities were interconnected during their crystallization. In many cases carbonates, sulfates, and/or fluorite have filled the cavities completely during the latest stages of fluid circulation. Circulation of hydrothermal fluids under open-system conditions is indicated by the presence of crosscutting barite-fluorite-quartz-sulfides-arsenates veins.
K feldspar (orthoclase) is the main rock-forming mineral of granophyric granite as well as the main crystallised mineral in miarolitic cavities, where it apperas as dark pink to brick-red, well-formed, short- to long-prismatic crystals; Manebach twin crystals are less common than the Baveno ones. Colourless to milky tabular albite crystals are sometimes overgrown on the side pinacoid (010).
At Cuasso al Monte, gadolinite-group minerals are zoned. In absence of a specific analysis on polished section of each crystal, on the basis of the available data published by Pezzotta et al. (1999) and Demartin et al. (2001), the following considerations may be helpful in leading to a verisimilar classification:
- subhedral crystals in primitive cavities can be considered gadolinite-(Y). They are hosted in feldspar and often associated with siderophyllite. These crystals are grey-brown in colour and zoned internally, with a darker core. The core consists of a REE-rich gadolinite-(Y) (with ΣREE>Y), the rim of gadolinite-(Y);
- euhedral crystals in highly evolved miarolitic cavities can be considered hingganite-(Y)-gadolinite-(Y). In the cavities, the presence of associated minerals as fluorite, clinochlore, and Y-REE carbonates indicates a well-developed, low-temperature hydrothermal event. These crystal are strongly zoned, with a darker core and a translucent white rim. The core, consisting of a REE-rich gadolinite-(Y) (with ΣREE>Y), is overgrown by gadolinite-(Y) with a high hingganite content and later hingganite-(Y). The visible surfaces of these crystals are therefore hingganite-(Y).
According to Demartin et al. (2001), all minerals tentatively classified in the past as "minasgeraesite" or "herderite" are invariably hingganite-(Y).
Scandium minerals are seldom found in miarolitic cavities. Bazzite appears as greyish-blue, hexagonal prismatic crystals. At the so-called “Tourmaline quarry”, one of the Val Cavallizza quarries, some hollow crystals of bazzite have been observed and sometimes the walls of their internal cavity are lined with tiny bertrandite crystals. The Cuasso al Monte bazzite is Mg-poor and contains a significant amount of cesium (up to 1.3 wt% Cs2O). Thortveitite occurs in association with "zinnwaldite" and a number of other accessory phases, including fluorite and hingganite-(Y). Crystals of thortveitite, white to pale blue in colour, are normally covered by a thick overgrowth of a spongy white cryptocrystalline aggregate composed of a mixture of minerals, mainly consisting of Sc, Zr, Y and HREE silicates. According to Gramaccioli et al. (2000), the thortveitite crystals are concentrically zoned: the concentration of Sc decreases from the core to the rim; on the contrary, the HREE concentration, as that of Y, strongly increases from the core to the rim.
In the granophyre miarolitic cavities synchysite group minerals (Ce- and Y-dominant synchysite and bastnäsite) often appear as paper-thin, bended, platy crystals aggregated into rose-like groups. Bastnäsite–(Ce) appears as pale flesh-coloured to red-brown, thick tabular, short- to long-prismatic crystals up to 1 mm.
Greyish-green pneumatolytic vein (greisens) also occur in the Cuasso al Monte granophyre. They are mainly composed of topaz, arsenopyrite, löllingite, cassiterite, sphalerite, chamosite, and various arsenates.
Warning: In very recent times some oustanding crystals of amethyst, a classic and highly sought mineral from the former Bianchi quarry (presently Gebel), attributed to an obscure find in the area of Cuasso al Monte, appeared on the market. Although these crystals, whose origin is Brandberg (Namibia), are very similar in morphology and habit to the authentic ones, some features (constant absence of dull faces, high abundance of double-terminated crystals, absence among the associated minerals of pink orthoclase, fluorite, dolomite and siderite, etc.) allow to distinguish them from those of Cuasso al Monte (Guastoni & Gentile, 2016).
Mineral ListMineral list contains entries from the region specified including sub-localities
97 valid minerals. 1 (TL) - type locality of valid minerals.
This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.
Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org
66 - 145 Ma
|Mesozoic sedimentary rocks|
Age: Cretaceous (66 - 145 Ma)
Comments: Dinaric Alps
Lithology: Sedimentary rocks
Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529. 
252.17 - 541 Ma
|Metamorphe Gesteine, meist Metasedimente|
252.17 - 298.9 Ma