Carbocalcio Quarry (Marmorea Quarry; San Lorenzo quarry), San Lorenzo, Valdieri, Cuneo Province, Piedmont, Italyi

Regional Level Types
Carbocalcio Quarry (Marmorea Quarry; San Lorenzo quarry)	Quarry
San Lorenzo	Village
Valdieri	Commune
Cuneo Province	Province
Piedmont	Region
Italy	Country

Large limestone quarry, opened in a large mass of recrystallised rocks of the Dauphinois sedimentary succession (Lower Cretaceous Lausa Limestone, Aptian-Cenomanian Marne Nere unit, and Upper Cretaceous Puriac Limestone), along the south slope of Monte La Piastra.

The recrystallisation mainly interests the Lower Cretaceous Lausa Limestone, which has been quarried in the past centuries as building and ornamental stone, commercially known as Bardiglio di Valdieri, at the Marmorea Royal Quarry (Real Cava Marmorea), originally a group of three quarries owned by the monarchs of the House of Savoy, which started operations in 1722. The quarry is now exploited by the company Carbocalcio Cuneese S.p.a. that produces CaCO₃ powders for industrial use.

The well-exposed Lausa Limestone is mainly represented by very pure white marble, with minor masses of banded grey marbles. In thin section, they result composed of a heterometric mosaic of 50-300 μm sized calcite crystals, commonly with polysynthetic twinning caused by low-temperature deformation. Rare silicate-bearing levels are present. They are composed of fine-grained phyllosilicates, K feldspar, albite and quartz. K feldspar (probably microcline, as it locally shows tartan twinning) forms subhedral elongated crystals, 500-2000 μm long, with the long axis parallel to the rock foliation. K feldspar crystals enclose iso-oriented phyllosilicates, which indicates a growth on a pre-existing foliation. They locally enclose also elongated euhedral albite crystals, 200-300 μm long, showing the typical Roc Tourné twinning. Silicate-bearing levels are folded. In the lower part of the recrystallised Lausa Limestone, levels with millimeter- to centimeter-sized dolostone clasts are present. Meter-sized dolostone masses are also present, probably aligned along the same stratigraphic interval. Macroscopically, the dolostone masses have a yellowish colour. Dolostone masses are crosscut by a close framework of centimeter-wide veins resulting from the brittle deformation of the dolomite mass, possibly already fractured, during the ductile deformation of the surrounding limestone. Veins are filled with quartz, calcite and a Fe-rich carbonate, probably ankerite. Quartz is the first cement phase and occurs as centimeter-sized euhedral crystals, whereas calcite forms centimeter-sized subhedral crystals. Ankerite is present as euhedral crystals, up to 1 cm large.

The Marne Nere unit (dark-coloured shales and marls), well exposed in the upper part of the Carbocalcio quarry, appears a thin interval (10-12 meters) of dark calcareous schists. In thin section they show a porphyroclastic structure, with large relict calcite crystals (probably echinoderm fragments) enveloped by the foliation. Rock foliation is defined by the alternation of carbonate levels, composed of 10-100 μm large calcite crystals, and levels rich in phyllosilicates and veils of opaque minerals. Quartz is locally present as subrounded grains, 20-100 μm in diameter, of probable detrital origin. Albite and pyrite are common accessory minerals, both forming euhedral crystals growing with no apparent relation with the rock foliation.

In the uppermost part of the Carbocalcio quarry, recrystallisation affects the lower part of the Puriac Limestone.

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